Could it be useful and would you have time and be willing to do another 'sharescreen' session, so that you can see what happens when?
Since this problem is quite new to me - until about 1 week ago - and I cannot find changed settings that cause the trouble, I wonder if one of the most recent MB updates is responsible. I use the latest version.
It's quite difficult to analyze the nature of the problems, I am not enough an expert to know what happens when and why.
In a way it seems that edit changes made in tracks are not instantly saved (as before), so after the edit you can not play it (track not found on expected location), nor can you make other edits.
In such case the only solution is to close MB, restart, then you find the SAVED first edit, but the following ones are not there.
In some cases (not in all, I think) the track has been duplicated or even tripled. One has ONE saved edit, the other two are obsolete.
It is especially visible in cases where artwork was added/replaced/deleted.
Hope this info brings the solution closer.
Please let me know what can be done...