I think I was mistaken, switching stuff about so much I think the DesktopGL build was using the release dll again so wasn’t showing this error. Though they may still be related issues.
However I have managed to create a reproducible test case for my problem. Basically when the player starts the game we had a line of code like this, calling the audio manager class I posted above.
engineSFX = Audio.PlaySound("sfx_rover_loop_00", true);
engineSFX.Pause();
And then in some begin method called when the race began, we did engineSFX.Play(), then when the race ended, we called engineSFX.Stop(true). For some reason this pause, followed by play, then calling stop, causes some kind of leak where it doesn’t get cleared out from the availableSourcesCollection in OpenALSoundController. After a while it’d run out of available sources and throw the InstancePlayLimitException. I’d say this is a bug as it essentially renders pausing the sounds unusable, so I will open up a separate issue on GitHub.