Happened to me on iOS 18 simulator on Xcode 16. Turns out I forgot to set it active before preparing any audio work when I refactored my code. Setting it active has resolved the issue. It actually makes sense being 0 Hz and 0 channel when it's inactive.

Not yet unfortunately but I’m going to have a look soon and if I find out something will post here as well. Today I’ve tested with a 20 input audio interface and Garage Band iOS version and it works pretty well so I think there should be a solution here and hope I’ll find one. Pretty strange that AVAudioSession doesn’t let me select the channel.