repeated syn error
For the past few weeks, sync is stopped with an error message (1573707942). The message is that a tmp file in my zotero/tmp directory cannot be deleted.
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Upgrade Storage
The only security software running is MS security. I tried, and the problem was not solved. Nothing changed recently as far as my security software is concerned.
You can also try installing Zotero Standalone, having it share your existing data directory (which is the default), and trying to sync with that. If something is interfering with Firefox's ability to write to the disk, Standalone might still work, and that might at least help narrow down the cause.