Can you provide a Debug ID for a sync that produces the error?

That’s not a Debug ID. Follow the link for instructions.

(3)(+0000000): UPLOAD BATCH:

(3)(+0000000): [
    "0": {
        "key": "QMS5MTNN"
        "version": 0
        "name": "0USGCKJa"
        "parentCollection": false
        "relations": {
            "dc:relation": [
                "0": "https://github.com/MuiseDestiny/zotero-citation#temporary-collection"
            ]
        }
    }

One of your plugins created invalid data in your database (dc:relation relations for collections). You'll need to contact the plugin developer for help.

Thanks for reporting this issue.
This was caused by Easier Citation 0.5.6. As part of the fix for #190, the plugin added a dc:relation marker to temporary collections so they could be cleaned up after an interrupted shutdown. This produced invalid Zotero sync data.
I have removed the affected 0.5.6 release. The fix no longer writes relations to temporary collections, stores their keys locally, and cleans up the old dc:relation data on startup.
I sincerely apologize for the inconvenience. Please continue to report any similar problems, and I will keep working on fixes.