Chrome extension problematic now in Vivaldi?

Does the issue happen on any specific site you can share?
All sites now.

Or is it all websites?
All

Could you elaborate further on when and where you're seeing delays?
Takes multiple clicks and sometimes 1Password entries will pop-up, sometimes not. Also, sometimes when they do pop-up for selection on the login field forms, they can't be selected.

Does the delay occur after you've just unlocked 1Password in the browser?
No - unlocked all the time and still delays.

Or does it occur after your device has been asleep/screensaver on
Nope, my laptop device never sleeps.

When you can't select an autofill item, is that an existing login item you're trying to fill, or a new generated password (Autofill option 'Use Suggested Password')?
Haven't seen it on new entries all that much. The delays and multiple attempts are on existing.

Could you try creating and filling a login item on our test site here? - https://fill.dev/form/login-simple
Will do.

Could you also try going to the Registration > Email page on that site, then click the Password field and see if you're able to click on 'Use Suggested Password'?
Will try and respond.

I will also record a video on this to give you a sense.