Summary On iOS build 24A446, an incoming CallKit VoIP call is reported and answered, but the system never creates or activates the CallKit audio session, so CXProviderDelegate provider:didActivateAudioSession: is never called. Both directions of call audio stay silent. The failure is inside callservicesd / audiomxd, before the app starts its audio unit. Once it starts, later calls from the same processes keep failing until the app process is killed.
App and device
- Bundle ID: us.zoom.videomeetings
- OS build: 24A446 (iPhone)
- Log: sysdiagnose_2026.10.16_11-15-45-0700_iPhone-OS_iPhone_24A446
- Sample call: 2026-10-15 13:29:06–13:29:22 PDT
- Processes in that window: Zoom PID 816, callservicesd PID 2474, audiomxd PID 115
How the user hits it The app is not in the foreground. A VoIP push wakes it and we call reportNewIncomingCallWithUUID:update:completion:. The user answers from the system incoming-call UI (phone locked or unlocked). The ringtone plays. After answer there is no call audio. The same failure then happens on later calls, including a call started from inside the app, until the Zoom process is killed. Signing out or rebooting only clears it temporarily. We cannot reproduce it in our lab. It became much more frequent after devices moved to this OS.
What the app does We configure one CXProvider (PlayAndRecord is applied when the system activates the session). We fulfill CXAnswerCallAction when the user answers. We start the voice audio unit only from provider:didActivateAudioSession:. We do not call AVAudioSession setActive: during this answered call. Our log line "ZMCallKitManager::didActivateAudioSession" is not present for this call.
System log for the sample call
13:29:06 — incoming call reported Zoom log: Provider was asked to report a new incoming call At that moment Zoom's existing primary session is sid:0x7304f, Zoom(816), 'prim', and the app is BackgroundRunning. callservicesd then fails while creating the CallKit session: audiomxd AVAudioSessionXPCServer.mm:231 -[AVAudioSessionRemoteXPCClient createProxySession:reply:] failed due to session lookup failure for SessionID 0x0 callservicesd AVAudioSession_iOS.mm:643 Creating proxy session failed, session ID = 0x0, NSOSStatusErrorDomain -50, "Session lookup failed" audiomxd ServerSessionManager.mm:192 Sibling session creation failed. Source sessionID: 0x0. SessionID is not valid. Source PID: 2474 audiomxd AVAudioSessionXPCServer.mm:1287 Session creation failed callservicesd SessionCore_Create.mm:92 AudioSession creation failed, NSOSStatusErrorDomain 2003329396, "Session creation failed in server" callservicesd Audio session not found for call. Returning nil The ringtone still plays. That audio is callservicesd's own session sid:0x732fa, category Ringtone/Default, which activates at 13:29:06.650. It is not the call session.
13:29:15 — user answers callservicesd: Performing answer request / Perform answer call callservicesd: No provider returned for descriptor callservicesd: Audio session not found for call. Returning nil callservicesd: Answer call action fulfilled callservicesd: Error retrieving AVAudioSession provider with ID 0 Sibling session creation fails again with Source sessionID 0x0, Source PID 2474. The ringtone session is stopped. From 13:29:15 to 13:29:22 there is no "action":"activate" for a CallKit call audio session, and no provider:didActivateAudioSession: notification to Zoom. Zoom's primary session 0x7304f is still inactive. Its category is updated to PlayAndRecord / VoiceChat, but it is not activated while this call is up.
13:29:22 — call ends Provider was asked to report that call ended with reason 2 callservicesd: Setting disconnected reason to remote hangup because ended reason is 2 sid:0x732fa callservicesd going inactive The call lasted about 7 seconds with no call audio session ever created.
13:29:33 — following call, same stuck state About 11 seconds later a CXStartCallAction is fulfilled. Zoom's own session then activates: sid:0x7304f, Zoom(816), 'prim' PlayAndRecord_WithBluetooth / VoiceChat, NonMixable, going active callservicesd still cannot build its session: "No existing proxy AVAudioSession interruption provider for ID 0, creating a new one" Session creation failed in server Error retrieving AVAudioSession provider with ID 0 Audio session not found for call So an app-side setActive: after the failed call does not repair the CallKit provider. The system session id remains 0x0.
How often it happens in this sysdiagnose Filtering the archive for the hard failure (not the generic "Audio session not found" line, which also appears on earlier days):
- "Sibling session creation failed. Source sessionID: 0x0": 93 hits, grouped into 57 bursts
- First burst: 2026-10-15 09:52:11 PDT
- Last burst: 2026-10-16 11:14:30 PDT (about a minute before this sysdiagnose was taken)
- "Error retrieving AVAudioSession provider with ID 0": 34 hits
- "Session creation failed in server": 93 hits
Every one of these sibling-session failures is Source PID 2474. callservicesd stays PID 2474 and audiomxd stays PID 115 across the whole window, including overnight. The bad session id is stuck in those daemons, not in one Zoom call object.
There is no log line in this archive showing callservicesd successfully activating a provider audio session for these calls.
Request Please confirm this is the known CallKit failure where didActivateAudioSession is not delivered because callservicesd cannot create the audio session (Session lookup failed / Session creation failed in server, session ID 0x0). Related public reports: Feedback FB19429215, "CallKit does not activate audio session after iOS 18.4.1", and the iOS 27 thread "iOS 27 CallKit didActivateAudioSession". DTS previously advised apps not to call setActive: themselves, because the CallKit session has higher priority and an app activation can fail or disturb system state. This log matches that: the session is never created, so there is nothing for the system to activate.
Please also advise which of these is safe on 24A446 when provider:didActivateAudioSession: does not arrive:
- Call CXProvider setConfiguration: again (same configuration) before every reportNewIncomingCallWithUUID:update:completion:.
- On a timeout, fail the unanswered CXAnswerCallAction so the CallKit state machine resets, without invalidating or recreating the CXProvider.
- Anything else that clears the stuck session ID 0x0 inside callservicesd without a device reboot.
I can provide another sysdiagnose if you need a logging profile installed before the next reproduction.