peter Hi Peter, thanks for the reply!
For the CPU I'm using an app called Status Lite.
I don't use Audiobus.
It happens when I've closed all apps I see in the app switcher, makes no difference. I don't know what else might be running in the background that I can't see, is there a way to see that? (Apologies, I'm fairly new to iOS).
The stuttering occurs when playing from the songs and playlists window, and also in the 'configure multitrack playback' window (if there are multiple tracks, if I mute other tracks it makes no difference, and all tracks do it).
The same imported file plays fine as a non-multitrack, but if I import as a track in a multitrack, even when it's the only track, it stutters.
I've tried changing the output from main to aux, no difference. I've uninstalled and reinstalled, no difference.
I only updated to iOS 15 yesterday to try and resolve the issue, the problem was occurring on the previous version too, I can't remember exactly what version it was unfortunately but it's not specific to iOS 15.
It's a weird one!