I have been having the same issue as JB above and have traced it back to the fact I was using the obsolete multi band compressor (the current version didn’t work on certain tracks).
I’ve had to remove all compression, export audio separately, then reimport as new audio track and add compression to the whole thing. A very broad stroke and not totally ideal but at least it’s been solved for now after many hours of playing with manual crossfades.
Has anyone else found this as the cause or are there possibly others as well?