Sorry, somehow missed your reply... As I wrote, this issue was not easily reproducible; I haven't seen it at all since iOS 18.4. Thanks, D.

Sure: as I wrote, this is beyond "edge case" — I was just curious about the sporadic main thread block... Thanks, D.

Hi, thank you for your feedback — I've opened FB 15232973 per your request. Thanks, D.

The throwing -10878 AVFoundation issue also occurs in macOS 12.3.1 — unfortunately, the Stack Overflow "answer" is not functionally equivalent since AVAudioOutputNode does not conform to AVAudioMixing.

The AVFoundation issue with throwing -10878 also occurs with macOS 12.3.1.

The throwing -10878 issue with AVAudioEngine and AVAudioMixerNode also occurs in macOS 12.3.1 — assuming it's been fixed in iOS, any idea if/when it'll be fixed on macOS too...? Thanks!