Error Report ID 644876571
Every time my Windows 11 desktop client syncs, I get a red exclamation point. I don't have to do anything to reproduce it except click the "sync" button.
Report ID: 644876571
Report ID: 644876571
Zotero shouldn't have let you create an attachment with a slash in the filename, but apparently that was allowed somehow when you added that file a few years ago.
We'll fix this, but for now you'd have to delete that attachment item and then delete it from the trash to allow the sync to go through. (You can make a copy of the PDF first and then add it back.)