PushToTalk session sometimes returns silence data after activation

Hello! Thank you for bringing the new iPhone experience with the PushToTalk framework.

I have a working walkie talkie app based on the PushToTalk framework. Everything works fine except for an intermittent bug that I face from time to time on different devices with different iOS versions, from iOS 18 to iOS 26.2 Beta.

Sometimes the app goes into a state where the AVAudioInputNode input node tap returns buffers with a constant size that contain only silence. Leaving and rejoining a channel helps, but relaunching or reinstalling (from Xcode) the app does not. Rebooting the device or deleting and reinstalling the app also helps.

I do not activate the audio session in my app. I only configure it on launch using

setCategory(.playAndRecord, options: [.defaultToSpeaker, .allowBluetooth])

So the flow is:

channelManager?.requestBeginTransmitting(channelUUID: globalChannelUUID)

func channelManager(
    _ channelManager: PTChannelManager,
    channelUUID: UUID,
    didBeginTransmittingFrom source: PTChannelTransmitRequestSource
)

func channelManager(
    _ channelManager: PTChannelManager,
    didActivate audioSession: AVAudioSession
) {
/// ...
 installTapAndStart()
}


private func installTapAndStart() {
    let inputNode = audioEngine.inputNode
    let hardwareFormat = inputNode.outputFormat(forBus: 0)
    
    guard let targetFormat = AVAudioFormat(
        commonFormat: .pcmFormatFloat32,
        sampleRate: configuration.audioSampleRate,
        channels: configuration.audioChannelsCount,
        interleaved: true
    ) else {
        handleError(RecorderError.invalidAudioFormat)
        return
    }
    
    let converter = AVAudioConverter(from: hardwareFormat, to: targetFormat)!
    
    print("[QUICOpusRecorder]: installTap")
    inputNode.installTap(onBus: 0, bufferSize: tapBufferSize, format: hardwareFormat) { [weak self] buffer, _ in
        guard let self else { return }
        // Here I handle audio data and sometimes get silence
    }
//...
        do {
            audioEngine.prepare()
            try audioEngine.start()
        } catch {
            print(" ⚠️ Audio engine start error: \(error)")
            handleError(error)
        }
}

Moreover, if the app is in the foreground and PushToTalk gets stuck in this “silence bug”, I can avoid relying on the PushToTalk flow and simulate audio session activation manually in code. In this case I do not request a transmission and do not use any PushToTalk related code, and the app captures audio data perfectly.

Once I leave the channel and rejoin it again, the issue is fixed and I start to receive non silent buffers of varying size, as expected.

It works for a while. It can work fine for a day or more, communicating without launching the app, or with the app in the foreground. But it can also go into the “silence” state 30 minutes after working normally.

I have no clue why this happens. The only thing I notice is that when the app is in this “stuck silence bug” state, iOS does not play its “chirp” system sound when audio recording starts.

P.S. Channel descriptor restoration code:

extension PushToTalkEngine: PTChannelRestorationDelegate {
    public func channelDescriptor(restoredChannelUUID channelUUID: UUID) -> PTChannelDescriptor {
        print("☀️ \(#function) channelUUID: \(channelUUID)")
        Task { @MainActor in
// Here I fetch more detailed channel data asynchronously 
            do {
                await initChannelManagerIfNeeded(channelUUID: channelUUID)
                let channelDescriptor = currentChannelDescriptor()
                lastChannelDescriptorName = channelDescriptor.name
                try await channelManager?.setChannelDescriptor(
                    channelDescriptor,
                    channelUUID: channelUUID
                )
            } catch {
                handleError(error)
            }

        }
        return PTChannelDescriptor(name: "Loading...", image: nil)
    }
}

    private func initChannelManagerIfNeeded(channelUUID: UUID? = nil) async {
        guard let channelUUID = channelUUID ?? currentUser?.globalChannelUUID else {
            print("❌ No global channel uuid found")
            return
        }
    
        do {
            guard channelManager == nil else {
                try await channelManager?.setTransmissionMode(.halfDuplex, channelUUID: channelUUID)
                return
            }
            channelManager = try await PTChannelManager.channelManager(
                delegate: self,
                restorationDelegate: self
            )
            try await channelManager?.setTransmissionMode(.halfDuplex, channelUUID: channelUUID)
        } catch {
            handleError(error)
        }
    }