Surprise, surprise! Yesterday I updated my macOS to Monterey Version 12.1. Today, with Xcode 13.1, I can play audio in Simulators with iOS 12.4 as I described in this thread one year ago. I suggest everybody to check if your problem is solved with macOS 12.1 as well.

Hi, I'm glad not to be the ony one with this issue. I'm using AVAudioEngine from iOS 9 to iOS 14. Since Big Sur Update I can only use simuated devices with iOS 14. Elder stages of development don't work either since the Update. I do not experience the failure on real devices. For my error stack I chose the same target as You( on iPhone 8 Plus simulator with iOS 11.4) and it seems to be pretty the same: xctest fehler 14:18:30.782700+0100 AudioHAL_Client HALB_IOBufferManager.cpp:226:GetIOBuffer:&#9;HALB_IOBufferManager::GetIOBuffer: the stream index is out of range xctest fehler 14:18:30.783822+0100 BoringSSL Function boringssl_session_errorlog: line 2881 [boringssl_session_read] SSL_ERROR_ZERO_RETURN(6): operation failed because the connection was cleanly shut down with a close_notify alert xctest fehler 14:18:30.784329+0100 BoringSSL Function boringssl_session_errorlog: line 2881 [boringssl_session_read] SSL_ERROR_ZERO_RETURN(6): operation failed because the connection was cleanly shut down with a close_notify alert xctest standard 14:18:30.784715+0100 <Beschreibung fehlt> TIC TCP Conn Event [1:0x7ffe4850b190]: 2 xctest standard 14:18:30.784950+0100 <Beschreibung fehlt> TIC TCP Conn Cancel [1:0x7ffe4850b190] xctest standard 14:18:30.785512+0100 [1 swr-swr3.cast.ybrid.io:443 stream, pid: 11336, url: https://swr-swr3.cast.ybrid.io/swr/swr3/ybrid, traffic class: 500, tls] cancelled [1.1 E5363C93-8B5F-4FE9-87AA-C4B1005A2FB6 582133952.53443<->'10 02 01 BB 3E 1B 3C 31 00 00 00 00 00 00 00 00'] Connected Path: satisfied (Path is satisfied), interface: en0 Duration: 10.228s, DNS @0.002s took 0.001s, TCP @0.006s took 0.026s, TLS took 0.069s bytes in/out: 5604/630, packets in/out: 7/3, rtt: 0.023s, retransmitted packets: 0, out-of-order packets: 0 xctest fehler 14:18:30.795025+0100 aqme 254: AQDefaultDevice (1): output stream 0: null buffer xctest standard 14:18:30.795265+0100 <Beschreibung fehlt> 505:&#9;buffer 0 ptr 0x0 size 4096 expected 4096 xctest fehler 14:18:30.795376+0100 aqme 1433: EXCEPTION thrown (-50): - xctest standard 14:18:30.795319+0100 <Beschreibung fehlt> TIC TCP Conn Cancel [2:0x7ffe4850d2c0] xctest standard 14:18:30.795969+0100 [2 swr-ybrid-edge-2004-fra-lg-cdn.cast.addradio.de:443 stream, pid: 11336, url: https://swr-ybrid-edge-2004-fra-lg-cdn.cast.addradio.de/swr/swr3/ybrid?_art=dj0yJmlwPTg4LjY5LjIxLjQ1JmlkPWljc2N4bC1jenNlMzJsbGImdD, traffic class: 500, tls] cancelled [2.1 F1421CF8-56AF-4995-9744-9C4D6FAA20CE 582133952.53444<->'10 02 01 BB D4 7A 89 FC 00 00 00 00 00 00 00 00'] Connected Path: satisfied (Path is satisfied), interface: en0 Duration: 10.109s, DNS @0.001s took 0.041s, TCP @0.048s took 0.019s, TLS took 0.114s bytes in/out: 202305/1062, packets in/out: 87/3, rtt: 0.349s, retransmitted packets: 0, out-of-order packets: 0 xctest fehler 14:18:30.797555+0100 <Beschreibung fehlt> Task <D405B35A-3E89-4D26-9ABC-EF9207FB4BB6>.<1> finished with error - code: -999 xctest fehler 14:18:36.572875+0100 aqme 177: timed out after 15.000s (0 1); suspension count=0 (IOSuspensions: ) xctest standard 14:18:36.573256+0100 aqme 390: AQME device AQDefaultDevice: client stopping after failed start: <CA_UISoundClientBase@0x7ffe4a2560f0>; running count now 0 xctest fehler 14:18:36.573558+0100 <Beschreibung fehlt> 239: CA_UISoundClientBase::StartPlaying: AddRunningClient failed (status = -66681). xctest standard 14:18:36.577838+0100 aurioc 1366: Starting AURemoteIO(0x7ffe4d000a40) output client:&#9;2 ch,&#9;44100 Hz, Float32, non-inter, output HW:&#9;2 ch,&#9;44100 Hz, Float32, non-inter input client:&#9; 2 ch,&#9;&#9;&#9;0 Hz, Int16, inter, input HW:&#9; 2 ch,&#9;&#9;&#9;0 Hz, Int16, inter xctest standard 14:18:36.578069+0100 aurioc 1376: work interval port 0x0 xctest standard 14:18:36.579318+0100 aqme 194: AQME device AQDefaultDevice: client starting: <RemoteIOClient@0x7ffe49813200(@0x7ffe498133e8); output; [11336]>; running count now 1 xctest standard 14:18:36.579504+0100 aqme 935: aqmeio@0x7ffe487b6700, device 0x58 (AQDefaultDevice), AudioDeviceStart (err 0) xctest fehler 14:18:36.716367+0100 AudioHAL_Client HALB_IOBufferManager.cpp:226:GetIOBuffer:&#9;HALB_IOBufferManager::GetIOBuffer: the stream index is out of range xctest fehler 14:18:36.716540+0100 AudioHAL_Client HALB_IOBufferManager.cpp:226:GetIOBuffer:&#9;HALB_IOBufferManager::GetIOBuffer: the stream index is out of range xctest fehler 14:18:36.728912+0100 aqme 254: AQDefaultDevice (1): output stream 0: null buffer xctest standard 14:18:36.729046+0100 <Beschreibung fehlt> 505:&#9;buffer 0 ptr 0x0 size 4096 expected 4096 xctest fehler 14:18:36.729125+0100 aqme 1433: EXCEPTION thrown (-50): - Hope we can find a solution. Florian