For the work around (I JUST FOUND THIS MORNING)...
I had to cut the nested sequence in half, then created a whole new multi-cam with that rear half of the nested sequence.
This actually WORKED. But my no means the fix.
I had to go back and re-edit my mulit-cam edit for that later half.
(No, I couldn't copy and paste the later half my edit from the first multi-cam edit...I had to do it all over again)
BUT... it did make the Canon work in sync.
are all of your sequences at the same framerate ?
Is your audio suddenly out of sync, or is it a progressive desync?
All the same frame rate. 24.
and yeah, it seems to suddenly get out of sync.
Did you see my work around? (above) to make it even more perplexing.
that's your workaround that made me think that it was probably a framerate issue.
But doesn't look like it.
Could you post a screen recording of the sound playing in sync in the nested seq, and not in the multicam seq?