The fix for this issue is now available in the latest update of InDesign – that is, InDesign 15.0.2.
Please update your InDesign application to get this fix.
Adobe InDesign team
An error occurred while saving the commentjd02 commented
I had this same issue just this week on Indesign 2020 in OS 10.15.7 and was losing lots of saved work. However I removed the shortcut (Command+Z) from Keyboard Shortcuts, and quit Indesign. Restarted Indesign and added the keyboard shortcut back in and it seems to have corrected the issue. Fingers crossed it stays this way.