That's the thing! Worked now.

I followed all the steps and removed from programdata and localappdata but it still isn't connecting. Even tried to disable steam guard. Any ideas?

Tried the mentioned solution on my desktop PC. It didn't at first, but finally made it work.
What did the trick was deleting the folder on my laptop too.
Apparently, you can only link accounts on one computer at a time?.

Having the same problem for over a week now. I've been using gog galaxy on my desktop and laptop for at least a year and it has been working flawlessly before the problems started. So there did not use to be a restriction to one computer at a time. I hope that has not changed.