Hi @Rolly, there is a sledgehammer method that I once outlined here: Audio sounds through only the left channel - #2 by Ulf
But that method is only good, if you use exclusively HSO or NotePerformer as playback template. As soon as you use custom instruments like e.g. Kontakt, then that method will destroy all your assignments and you have to recreate all by hand again.
The way that I fixed your project is that I modified the audio engine data, instead of deleting it all together. For me it is easy, but it needs a Hex-Editor to do that, and one needs to have a bit of technical understanding, which I can’t assume everyone to have. Maybe I’ll write down a recipe at some stage for tech savvy people. Until then, send me your projects for fixing. I really don’t mind.