Hi,
Just to add that I recently is meeting the same issue. By recently I actually mean 1 or up to 2 months. This is fairly weird because I did reinstall opera a little before and I had no issue. As far as I can remember, It appeared while I was properly logged. Was it after a backup ? Is it linked to a degraded service ? I can't tell for sure.
What I can tell for sure is as soon as I log with my opera credentials it freezes the browser for quite some time. I just retried though and it froze and successfully logged and synced. Let's see what experience will it come with in usage.