I know there's a similar topic in the forum but the solution eludes me.
My problem is that when enabling the extension the button appears and disappears a few indeterminate number of times until it finally stays but remains unresponsive. The first button that appears looks different  than the rest appearing in the sequence . The action looks similar to what is described in a clip posted on the Vivaldi forum.
I have tried reinstalling the extension but that didn't help.
It does work in Chrome, Safari and Firefox.
I've had similar problems before but don't remember how it was solved.
1Password extension 220.127.116.11