I had the same issue, all I could do is delete the song and start over with the audio files i saved, I finished the project in one sitting and exported audio and saved numerous times no trouble, but when I saved and exited and out of curiosity re-opened the song I got this message;
Could not complete your request because Assertion in "E:\ Code\ 222437\ ProTools\ App\ Networking\ DNet\ PTCC\ PTCCLib\ PTCCLib_Services.cpp", line 2650.
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It might be worth noting that I keep getting messages asking whether or not i want to save to the could or local and that I am saving over or replacing an already existing cloud copy.
Hope this helps, this issue is ridiculous and destroying my music
