JavaScript Error: "uncaught exception: Invalid response from server"

cdias
The sync arrow has been spinning all day and I finally received the following error messages:
[JavaScript Error: "The service is not available. Please try again later." {file: "chrome://zotero/content/xpcom/sync.js" line: 2112}]

[JavaScript Error: "uncaught exception: Invalid response from server"]

[JavaScript Error: "The service is not available. Please try again later." {file: "chrome://zotero/content/xpcom/sync.js" line: 2112}]

[JavaScript Error: "uncaught exception: Invalid response from server"]

I receive the same messages twice, under error IDs: 2039026169 and 836573005.

I've restarted Firefox multiple times as well rebooting my computer. Is there anything else I can try to resolve this?
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