@t3owner There seems to be data from the first installation of Opera somewhere on Android devices that won‘t be deleted by clearing data and/or cache. Maybe they are even stored in the cloud as in your case.
Try the following, it worked for me today: Deinstall Opera and simply reinstall it. But before starting it again, simply disconnect from every network, so that Opera only fetches data from the device. (For me appeared a Speed Dial from a former setup).
Then go to „auth.opera.com“ which will not load of course. Then connect to your internet and type in your credentials. Pass the captcha if it appears again, it should work after the second trial.
I suppose there‘s a conflict, as Opera‘s somehow assuming that you‘re already logged in.
P.S. It seems to be quite more difficult, if you have changed your Opera account (or even deleted it). You should go by the credentials that worked last time.
If someone would know where this „hidden data“ may be stored, she or he might be very welcome.