FOUND THE SOLUTION/CAUSE

For me its this app which triggered random linkedin pop ups which are instantly closing :

Find website used fonts
https://chrome.google.com/webstore/detail/find-website-used-fonts/lnebjgioddkafaldaaeooeghlcholnnp

I just deactivated every extension I have in opera, and reactivated extensions one by one in 2-5mins intervalls.

I got this extension through operas official Install Chrome Extensions

If you have this extension, you should delete it and after that it will not happen again. But if it's still happening, or you dont even have it installed, you should deactivate every extension and reactivate them one by one.

If its another extension which is causing this, please tell us which one it is.