The fix for this issue is available in the latest update of InDesign version 15.0.3
Please update your InDesign application to this version to get the fix.
Adobe InDesign team
An error occurred while saving the commentDoug Shemilt commented
This solution by anonymous fixed this issue for me:
"I had this same issue and I found the culprit, for me at least. Some of the links a colleague had placed had file path names that were excessively long. I am not sure of the character limit on overall paths or individual file names but I found several ridiculous ones in my document, renamed and resolved the issue. "
I just changed the width of the Name column in Windows File Explorer to find the most obvious super-long files. Luckily I only had 10 or so files of crazy length, as there's no way of sorting by name length