We’re seeing the exact same issue, minus the logs from augraph and aurioc:
HALB_IOBufferManager_Client::GetIOBuffer: the stream index is out of range
HALB_IOBufferManager_Client::GetIOBuffer: the stream index is out of range
HALB_IOBufferManager_Client::GetIOBuffer: the stream index is out of range
[aqme] 255: AQDefaultDevice (1): output stream 0: null buffer
[aqme] 1778: EXCEPTION thrown (-50): error != 0
Start: Mach message timeout. Apparently deadlocked. Aborting now.
CoreSimulator 725.10.3 - Device: iPad Pro (12.9-inch) (4th generation) - Runtime: iOS 14.0 (18A5301v) - DeviceType: iPad Pro (12.9-inch) (4th generation)
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Submitted FB7761200:
Initializing audio I/O using Xcode 12.0 beta (12A6159) on the iOS Simulator results the app crashing with the following console logs:
HALBIOBufferManagerClient::GetIOBuffer: the stream index is out of range
HALBIOBufferManagerClient::GetIOBuffer: the stream index is out of range
[aqme] 255: AQDefaultDevice (1): output stream 0: null buffer
[aqme] 1778: EXCEPTION thrown (-50): error != 0
Initialize: Mach message timeout. Apparently deadlocked. Aborting now.
This can be easily reproduced e.g. with the "AUV3Filter iOS" app that is part of this sample project:
https://developer.apple.com/documentation/audiotoolbox/audio_unit_v3_plug-ins/creating_custom_audio_effects
Steps to reproduce:
Launch app
Expected results:
App launches
Actual results:
App crashes in AURemoteIO::Initialize()
Backtrace:
thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
		frame #0: 0x000000010515f33a libsystem_kernel.dylib`__pthread_kill + 10
		frame #1: 0x00000001051bce60 libsystem_pthread.dylib`pthread_kill + 430
		frame #2: 0x0000000104eb7c24 libsystem_c.dylib`abort + 120
		frame #3: 0x00000001087655c9 AudioToolboxCore`_ReportRPCTimeout(char const*, int) + 90
		frame #4: 0x0000000126a08bd9 libEmbeddedSystemAUs.dylib`_CheckRPCError(char const*, int, int) + 92
		frame #5: 0x0000000126a054e0 libEmbeddedSystemAUs.dylib`AURemoteIO::Initialize() + 1878
		frame #6: 0x0000000126a1eec6 libEmbeddedSystemAUs.dylib`AUBase::DoInitialize() + 36
		frame #7: 0x00000001269a547f libEmbeddedSystemAUs.dylib`AUMethodInitialize(void*) + 59
		frame #8: 0x000000010885a1bb AudioToolboxCore`-[AUAudioUnitV2Bridge allocateRenderResourcesAndReturnError:] + 77
		frame #9: 0x00000001064c5dbf AVFAudio`AUInterfaceBaseV3::Initialize() + 45
		frame #10: 0x0000000106469ef9 AVFAudio`AUGraphNodeBase::Initialize() + 29
		frame #11: 0x00000001064478a1 AVFAudio`AVAudioEngineGraph::PerformCommand(AUGraphNodeBaseV3&, AVAudioEngineGraph::ENodeCommand, void*, unsigned int) const + 365
		frame #12: 0x000000010644f63e AVFAudio`AVAudioEngineGraph::Initialize(NSError) + 1642
		frame #13: 0x00000001064c422f AVFAudio`AVAudioEngineImpl::Initialize(NSError) + 201
		frame #14: 0x00000001064bf36e AVFAudio`-[AVAudioEngine prepare] + 66
	* frame #15: 0x0000000101582aaf AUv3FilterFramework`SimplePlayEngine.init(self=0x0000600002a540c0) at SimplePlayEngine.swift:59:16
...
Same here. Submitted via Feedback Assistant as FB8893389.
Thank you aDope, the trick with mapping the shortcut using the NumPad works great, and you can even use the normal Cmd-Shift-7 shortcut without the NumPad after.