I have solution for cookies missmatch. I try this steps and more days is all ok - before it return error in one day.

1. Go to Settings and check that browser is default.
2. Go to Windows setting and check that is Opera set as default for browsing too - no only with text - but with logo too! If no, try change to Edge or IE and back.
3. Go to Opera settings - delete cookies (for sure delete all) and delete cache

Problem - I think - is that OS has bad setting for default browser and Opera see that is first running "as default" and trying reload settings from other browser - with cookies too. So you import old google cookies from old browser and have new google cokies from Opera - and this is missmatch.

Maybe it is bug?

I hope, that this help you all with this problems

Pavel