Hi Stuart,
To narrow down the root cause of the issue, I'd like to confirm the following information:
1. Which application folder did you open when encountering the issue?
2. Did the issue only occur in a specific file? Could you try opening another file?
3. Did you try clearing all process on your Mac to see if it helps?
4. Can you share a full screenshot of the error message with us? To upload screenshots, please click Use rich Formatting in this thread and select the Insert/Edit Media icon.
5. Do you mean the issue occur in the affected file in SharePoint Online libraries when connecting SharePoint Sites via Document Connection on your Mac?
After getting the information above, we'll proceed further. Thanks for your time.
Regards,
Alice Wang