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"We are aware that there is an issue with the Collaborate service at this time.
Please bear with us while we diagnose and fix the problem."
I've just received a reply to my support ticket that confirms the issue. Unity knows about it and is working to fix the issue.
It seems that the Collab team is located in Seattle so we probably need to wait for them to wake up and fix it :(
Same here! Removing the folder did not solve the issue. Downloading stuck on 0% on all devices at our office.
Maybe it is dead.