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 commentdutchdesign commented
Problem clearly has multiple possible sources. I was able to solve it by tracking down long file-paths for some images. moved the files closer to the root folder (shorter path) and relinked. Then I was able to export to pdf again.