Debug ID is D826631647
Hello, my problem is, that the last attachments (PDF files) are not synchronized respectively uploaded. According to your documentation (https://www.zotero.org/support/kb/files_not_syncing), I tried Sync → Reset pane of the Zotero settings on Computer A and select Reset File Sync History for my library. As this did not work, I submitted the debug file (D826631647) and this discussion. Thanks for your help.
Upgrade Storage
You've now upgraded, but you need to sync the computer where the files actually exist so that they get uploaded.