@leocg No, manually entering the login does not resolve the issue.
The errors depend on the site, some give bad request with headers too long exception, others will just load forever. Some just redirect to a generic "we're having technical difficulties" page. These issues only seem to arise when dealing with finance or payments, I haven't seen it happen on most other sites. Maybe an OAuth related problem (wild guess though).
1Password sometimes won't find any login information after signing in, but it feels random.
Trying the same thing in Google Chrome will have no issue. It didn't use to be a problem in Opera GX, but the last few months I noticed this issue more and more.