[JavaScript Error: "Upload request 1/ZXUNWHCX failed"]
[JavaScript Error: "Group with libraryID 1 does not exist" {file: "chrome://zotero/content/xpcom/data/groups.js" line: 108}]

Can you provide a Debug ID (different from a Report ID) for a sync attempt that triggers this?

After you've provided that, just restarting Zotero might fix it. But please provide the Debug ID first.