Fix for this issue is now available in the latest update of InDesign 2020 – that is, InDesign 15.1.2
In the Creative Cloud Desktop application, click on the Updates section on the left. You should be able to see the Update available for InDesign. Please update your InDesign application to this version to try out the fix.
Let us know in the comments section if you still face this problem.
Adobe InDesign Team
An error occurred while saving the commentLori Delappe commented
I have the latest version and just got the same error again today. The PDF is not open anywhere and has been closed for 20 minutes. I do not have time to regularly close ID in order to reset this feature. What can I do?