I've the same problem, and I did the same thing to resolve it but nothing :|
And I don't know why, but some website keep me connected like Instagram or the Nexus (for video games mods).
And Twitter, Facebook, my google account (Very annoying for youtube) don't keep me connected.
I've this problem since I've reinstalled Windows (new stuff for my computer) so, the installation was necessarily clean
If someone have a solution ? I have Opera since 8-9 years and it's the first time I have this :|