diff --git a/changes/fix-jellyfin-modern-auth.md b/changes/fix-jellyfin-modern-auth.md
index 4eb756a0..f4180fb7 100644
--- a/changes/fix-jellyfin-modern-auth.md
+++ b/changes/fix-jellyfin-modern-auth.md
@@ -2,3 +2,4 @@ type: fixed
 area: jellyfin
 
 - Authenticate Jellyfin playback, subtitle, artwork, and remote-control socket URLs with the `ApiKey` query parameter and stop sending the legacy `X-Emby-Token` and `X-Emby-Authorization` headers, so the integration keeps working on Jellyfin 12 where legacy authorization is disabled by default.
+- Keep the cast-target websocket alive by answering Jellyfin keep-alive requests and reconnect when the server stops replying, so "Play on SubMiner" keeps working on Jellyfin 12 instead of silently dying about a minute after connecting. Failed playback progress and stop reports are now logged as warnings.
diff --git a/src/core/services/jellyfin-remote.test.ts b/src/core/services/jellyfin-remote.test.ts
index 7877cadd..69c358cd 100644
--- a/src/core/services/jellyfin-remote.test.ts
+++ b/src/core/services/jellyfin-remote.test.ts
@@ -4,6 +4,17 @@ import { buildJellyfinTimelinePayload, JellyfinRemoteSessionService } from './je
 
 class FakeWebSocket {
   private listeners: Record<string, Array<(...args: unknown[]) => void>> = {};
+  sent: string[] = [];
+  terminated = false;
+
+  send(data: string): void {
+    this.sent.push(data);
+  }
+
+  terminate(): void {
+    this.terminated = true;
+    this.emit('close');
+  }
 
   on(event: string, listener: (...args: unknown[]) => void): this {
     if (!this.listeners[event]) {
@@ -356,3 +367,114 @@ test('advertiseNow validates server registration using Sessions endpoint', async
   assert.equal(ok, true);
   assert.ok(calls.some((url) => url.endsWith('/Sessions')));
 });
+
+test('answers ForceKeepAlive with KeepAlive messages on the advertised cadence', () => {
+  const sockets: FakeWebSocket[] = [];
+  const timers: Array<{ handler: () => void; delay: number }> = [];
+
+  const service = new JellyfinRemoteSessionService({
+    serverUrl: 'http://jellyfin.local',
+    accessToken: 'token-ka',
+    deviceId: 'device-ka',
+    webSocketFactory: () => {
+      const socket = new FakeWebSocket();
+      sockets.push(socket);
+      return socket as unknown as any;
+    },
+    fetchImpl: (async () => new Response(null, { status: 200 })) as typeof fetch,
+    setTimer: ((handler: () => void, delay?: number) => {
+      timers.push({ handler, delay: Number(delay) });
+      return timers.length as unknown as ReturnType<typeof setTimeout>;
+    }) as typeof setTimeout,
+    clearTimer: (() => undefined) as typeof clearTimeout,
+  });
+
+  service.start();
+  sockets[0]!.emit('open');
+  assert.deepEqual(sockets[0]!.sent, ['{"MessageType":"KeepAlive"}']);
+  assert.equal(timers[0]!.delay, 30_000);
+
+  sockets[0]!.emit('message', JSON.stringify({ MessageType: 'ForceKeepAlive', Data: 20 }));
+  assert.equal(sockets[0]!.sent.length, 2);
+  assert.equal(timers.at(-1)!.delay, 10_000);
+
+  timers.at(-1)!.handler();
+  assert.equal(sockets[0]!.sent.length, 3);
+});
+
+test('reconnects when the server stops answering keep-alives', () => {
+  let now = 1_000_000;
+  const sockets: FakeWebSocket[] = [];
+  const timers: Array<() => void> = [];
+  const warnings: string[] = [];
+
+  const service = new JellyfinRemoteSessionService({
+    serverUrl: 'http://jellyfin.local',
+    accessToken: 'token-lost',
+    deviceId: 'device-lost',
+    webSocketFactory: () => {
+      const socket = new FakeWebSocket();
+      sockets.push(socket);
+      return socket as unknown as any;
+    },
+    fetchImpl: (async () => new Response(null, { status: 200 })) as typeof fetch,
+    getNow: () => now,
+    logWarn: (message) => {
+      warnings.push(message);
+    },
+    reconnectBaseDelayMs: 100,
+    setTimer: ((handler: () => void) => {
+      timers.push(handler);
+      return timers.length as unknown as ReturnType<typeof setTimeout>;
+    }) as typeof setTimeout,
+    clearTimer: (() => undefined) as typeof clearTimeout,
+  });
+
+  service.start();
+  sockets[0]!.emit('open');
+
+  // Two silent ticks are still within the 90s tolerance; the third marks the socket lost.
+  now += 30_000;
+  timers.shift()!();
+  now += 30_000;
+  timers.shift()!();
+  assert.equal(sockets[0]!.sent.length, 3);
+  assert.equal(sockets[0]!.terminated, false);
+
+  now += 30_000;
+  timers.shift()!();
+  assert.equal(sockets[0]!.terminated, true);
+  assert.equal(service.isConnected(), false);
+  assert.equal(warnings.length, 1);
+
+  timers.shift()!();
+  assert.equal(sockets.length, 2);
+});
+
+test('warns once per failing timeline endpoint until it recovers', async () => {
+  const warnings: string[] = [];
+  let status = 400;
+
+  const service = new JellyfinRemoteSessionService({
+    serverUrl: 'http://jellyfin.local',
+    accessToken: 'token-warn',
+    deviceId: 'device-warn',
+    webSocketFactory: () => new FakeWebSocket() as unknown as any,
+    fetchImpl: (async () => new Response(null, { status })) as typeof fetch,
+    logWarn: (message) => {
+      warnings.push(message);
+    },
+  });
+  const state = { itemId: 'item-1', positionTicks: 10, playMethod: 'DirectPlay' };
+
+  assert.equal(await service.reportStopped(state), false);
+  assert.equal(await service.reportStopped(state), false);
+  assert.equal(warnings.length, 1);
+  assert.match(warnings[0]!, /Sessions\/Playing\/Stopped/);
+
+  status = 200;
+  assert.equal(await service.reportStopped(state), true);
+  status = 500;
+  assert.equal(await service.reportStopped(state), false);
+  assert.equal(warnings.length, 2);
+});
diff --git a/src/core/services/jellyfin-remote.ts b/src/core/services/jellyfin-remote.ts
index cd0ce605..0d484c6e 100644
--- a/src/core/services/jellyfin-remote.ts
+++ b/src/core/services/jellyfin-remote.ts
@@ -45,9 +45,22 @@ interface JellyfinRemoteSocket {
   on(event: 'close', listener: () => void): this;
   on(event: 'error', listener: (error: Error) => void): this;
   on(event: 'message', listener: (data: unknown) => void): this;
+  send(data: string): void;
+  terminate?(): void;
   close(): void;
 }
 
+// Jellyfin advertises its keep-alive timeout in the ForceKeepAlive message (60s by default),
+// drops sockets that stay silent past it, and since 12.0 also detaches the session's remote
+// controller when that happens. The drop never reaches the client as a close frame, so the
+// client has to keep sending KeepAlive and treat missing replies as a dead connection.
+const DEFAULT_KEEP_ALIVE_TIMEOUT_MS = 60_000;
+const KEEP_ALIVE_LOST_FACTOR = 1.5;
+
+function unrefTimer(timer: ReturnType<typeof setTimeout>): void {
+  (timer as unknown as { unref?: () => void }).unref?.();
+}
+
 type JellyfinRemoteSocketHeaders = Record<string, string>;
 
 export interface JellyfinRemoteSessionServiceOptions {
@@ -77,6 +90,9 @@ export interface JellyfinRemoteSessionServiceOptions {
   deviceName?: string;
   onConnected?: () => void;
   onDisconnected?: () => void;
+  logWarn?: (message: string, details?: unknown) => void;
+  keepAliveTimeoutMs?: number;
+  getNow?: () => number;
 }
 
 function normalizeServerUrl(serverUrl: string): string {
@@ -196,6 +212,12 @@ export class JellyfinRemoteSessionService {
   private readonly authHeader: string;
   private readonly onConnected?: () => void;
   private readonly onDisconnected?: () => void;
+  private readonly logWarn?: (message: string, details?: unknown) => void;
+  private readonly now: () => number;
+  private keepAliveTimeoutMs: number;
+  private keepAliveTimer: ReturnType<typeof setTimeout> | null = null;
+  private lastInboundAtMs = 0;
+  private readonly failedRequestPaths = new Set<string>();
 
   private readonly reconnectBaseDelayMs: number;
   private readonly reconnectMaxDelayMs: number;
@@ -233,6 +255,12 @@ export class JellyfinRemoteSessionService {
     });
     this.onConnected = options.onConnected;
     this.onDisconnected = options.onDisconnected;
+    this.logWarn = options.logWarn;
+    this.now = options.getNow ?? Date.now;
+    this.keepAliveTimeoutMs = Math.max(
+      1000,
+      options.keepAliveTimeoutMs ?? DEFAULT_KEEP_ALIVE_TIMEOUT_MS,
+    );
     this.reconnectBaseDelayMs = Math.max(100, options.reconnectBaseDelayMs ?? 500);
     this.reconnectMaxDelayMs = Math.max(
       this.reconnectBaseDelayMs,
@@ -250,6 +278,7 @@ export class JellyfinRemoteSessionService {
   public stop(): void {
     this.running = false;
     this.connected = false;
+    this.stopKeepAlive();
     if (this.reconnectTimer) {
       this.clearTimer(this.reconnectTimer);
       this.reconnectTimer = null;
@@ -298,12 +327,15 @@ export class JellyfinRemoteSessionService {
       if (this.socket !== socket || !this.running) return;
       this.connected = true;
       this.reconnectAttempt = 0;
+      this.lastInboundAtMs = this.now();
+      this.startKeepAlive(socket, this.keepAliveTimeoutMs);
       this.onConnected?.();
       void this.postCapabilities();
     });
 
     socket.on('message', (rawData) => {
-      this.handleInboundMessage(rawData);
+      this.lastInboundAtMs = this.now();
+      this.handleInboundMessage(socket, rawData);
     });
 
     const handleDisconnect = () => {
@@ -311,6 +343,7 @@ export class JellyfinRemoteSessionService {
       disconnected = true;
       if (this.socket === socket) {
         this.socket = null;
+        this.stopKeepAlive();
       }
       this.connected = false;
       this.onDisconnected?.();
@@ -323,6 +356,51 @@ export class JellyfinRemoteSessionService {
     socket.on('error', handleDisconnect);
   }
 
+  private startKeepAlive(socket: JellyfinRemoteSocket, timeoutMs: number): void {
+    this.stopKeepAlive();
+    this.keepAliveTimeoutMs = timeoutMs;
+    this.sendKeepAlive(socket);
+    this.scheduleKeepAliveTick(socket);
+  }
+
+  private scheduleKeepAliveTick(socket: JellyfinRemoteSocket): void {
+    const intervalMs = Math.max(1000, Math.floor(this.keepAliveTimeoutMs / 2));
+    const timer = this.setTimer(() => {
+      this.keepAliveTimer = null;
+      if (this.socket !== socket || !this.running) return;
+      const silentForMs = this.now() - this.lastInboundAtMs;
+      if (silentForMs >= this.keepAliveTimeoutMs * KEEP_ALIVE_LOST_FACTOR) {
+        this.logWarn?.('Jellyfin remote websocket stopped answering keep-alives; reconnecting.');
+        // Dropping the socket raises 'close', which schedules the reconnect.
+        if (socket.terminate) {
+          socket.terminate();
+        } else {
+          socket.close();
+        }
+        return;
+      }
+      this.sendKeepAlive(socket);
+      this.scheduleKeepAliveTick(socket);
+    }, intervalMs);
+    unrefTimer(timer);
+    this.keepAliveTimer = timer;
+  }
+
+  private stopKeepAlive(): void {
+    if (this.keepAliveTimer) {
+      this.clearTimer(this.keepAliveTimer);
+      this.keepAliveTimer = null;
+    }
+  }
+
+  private sendKeepAlive(socket: JellyfinRemoteSocket): void {
+    try {
+      socket.send(JSON.stringify({ MessageType: 'KeepAlive' }));
+    } catch (error) {
+      this.logWarn?.('Failed to send Jellyfin remote keep-alive.', error);
+    }
+  }
+
   private scheduleReconnect(): void {
     const delay = Math.min(
       this.reconnectMaxDelayMs,
@@ -397,16 +475,38 @@ export class JellyfinRemoteSessionService {
         },
         body: JSON.stringify(payload),
       });
+      this.noteRequestOutcome(path, response.ok ? null : `HTTP ${response.status}`);
       return response.ok;
-    } catch {
+    } catch (error) {
+      this.noteRequestOutcome(path, error);
       return false;
     }
   }
 
-  private handleInboundMessage(rawData: unknown): void {
+  // Warn once per path while it keeps failing so a rejected stop report is visible in the
+  // log without a warning per progress tick.
+  private noteRequestOutcome(path: string, failure: unknown): void {
+    if (failure === null) {
+      this.failedRequestPaths.delete(path);
+      return;
+    }
+    if (this.failedRequestPaths.has(path)) return;
+    this.failedRequestPaths.add(path);
+    this.logWarn?.(`Jellyfin remote request failed: POST ${path}`, failure);
+  }
+
+  private handleInboundMessage(socket: JellyfinRemoteSocket, rawData: unknown): void {
     const message = parseInboundMessage(rawData);
     if (!message) return;
     const messageType = message.MessageType;
+    if (messageType === 'ForceKeepAlive') {
+      const seconds = Number(message.Data);
+      const timeoutMs =
+        Number.isFinite(seconds) && seconds > 0 ? seconds * 1000 : this.keepAliveTimeoutMs;
+      this.startKeepAlive(socket, timeoutMs);
+      return;
+    }
+    if (messageType === 'KeepAlive') return;
     const payload = parseMessageData(message.Data);
     if (messageType === 'Play') {
       this.onPlay?.(payload);
diff --git a/src/main/runtime/composers/jellyfin-remote-composer.ts b/src/main/runtime/composers/jellyfin-remote-composer.ts
index 2de85547..000ee004 100644
--- a/src/main/runtime/composers/jellyfin-remote-composer.ts
+++ b/src/main/runtime/composers/jellyfin-remote-composer.ts
@@ -91,6 +91,7 @@ export function composeJellyfinRemoteHandlers(
       getNow: options.getNow,
       ticksPerSecond: options.ticksPerSecond,
       logDebug: options.logDebug,
+      logWarn: options.logWarn,
     });
   const reportJellyfinRemoteProgress = createReportJellyfinRemoteProgressHandler(
     buildReportJellyfinRemoteProgressMainDepsHandler(),
diff --git a/src/main/runtime/jellyfin-remote-main-deps.ts b/src/main/runtime/jellyfin-remote-main-deps.ts
index d5b4dd20..ed3ca45d 100644
--- a/src/main/runtime/jellyfin-remote-main-deps.ts
+++ b/src/main/runtime/jellyfin-remote-main-deps.ts
@@ -75,5 +75,6 @@ export function createBuildReportJellyfinRemoteStoppedMainDepsHandler(
     getNow: deps.getNow ? () => deps.getNow?.() ?? Date.now() : undefined,
     ticksPerSecond: deps.ticksPerSecond,
     logDebug: (message: string, error: unknown) => deps.logDebug(message, error),
+    ...(deps.logWarn ? { logWarn: (message: string) => deps.logWarn?.(message) } : {}),
   });
 }
diff --git a/src/main/runtime/jellyfin-remote-playback.ts b/src/main/runtime/jellyfin-remote-playback.ts
index 8ea0c6c9..54ebd8fa 100644
--- a/src/main/runtime/jellyfin-remote-playback.ts
+++ b/src/main/runtime/jellyfin-remote-playback.ts
@@ -203,6 +203,7 @@ export type JellyfinRemoteStoppedReporterDeps = {
   getNow?: () => number;
   ticksPerSecond: number;
   logDebug: (message: string, error: unknown) => void;
+  logWarn?: (message: string) => void;
 };
 
 export function createReportJellyfinRemoteStoppedHandler(deps: JellyfinRemoteStoppedReporterDeps) {
@@ -244,7 +245,7 @@ export function createReportJellyfinRemoteStoppedHandler(deps: JellyfinRemoteSto
       } catch (error) {
         deps.logDebug('Failed to report Jellyfin remote final progress', error);
       }
-      await session.reportStopped({
+      const reported = await session.reportStopped({
         itemId: playback.itemId,
         mediaSourceId: playback.mediaSourceId,
         positionTicks,
@@ -254,6 +255,11 @@ export function createReportJellyfinRemoteStoppedHandler(deps: JellyfinRemoteSto
         subtitleStreamIndex: playback.subtitleStreamIndex,
         eventName: 'stop',
       });
+      if (reported === false) {
+        deps.logWarn?.(
+          `Jellyfin did not accept the playback stop report for item ${playback.itemId}; the server may keep showing it as playing.`,
+        );
+      }
     } catch (error) {
       deps.logDebug('Failed to report Jellyfin remote stop', error);
     } finally {
diff --git a/src/main/runtime/jellyfin-remote-session-lifecycle.ts b/src/main/runtime/jellyfin-remote-session-lifecycle.ts
index 233f94af..a7b5759c 100644
--- a/src/main/runtime/jellyfin-remote-session-lifecycle.ts
+++ b/src/main/runtime/jellyfin-remote-session-lifecycle.ts
@@ -38,6 +38,7 @@ type JellyfinRemoteServiceOptions = {
   };
   onConnected: () => void;
   onDisconnected: () => void;
+  logWarn?: (message: string, details?: unknown) => void;
   onPlay: (payload: JellyfinRemoteEventPayload) => void;
   onPlaystate: (payload: JellyfinRemoteEventPayload) => void;
   onGeneralCommand: (payload: JellyfinRemoteEventPayload) => void;
@@ -110,6 +111,7 @@ export function createStartJellyfinRemoteSessionHandler(deps: {
       onDisconnected: () => {
         deps.logWarn('Jellyfin remote websocket disconnected; retrying.');
       },
+      logWarn: (message, details) => deps.logWarn(message, details),
       onPlay: (payload) => {
         void deps.handlePlay(payload).catch((error) => {
           deps.logWarn('Failed handling Jellyfin remote Play event', error);