After changing a login's password, 1Password "Open and fill" failed for that login in Safari
Recently I've changed my password for a couple of logins, and of course saved the new passwords in 1Password. When I immediately tested the new passwords with "Open and fill" (regardless of whether I launched "Open and fill" from the main app or the Safari extension), the logins failed (the websites reported the standard "wrong username and/or password").
But when I copied the new password from the main 1Password app to the clipboard and pasted it in, the login credentials were accepted.
When I revealed the password in the main app, the new password was there. But when I revealed the password in the Safari extension, the old password showed.
It appears that the Safari extension was pasting the old password into the password field - I confirmed that by using the "show password" option that one of the sites gave.
This persisted for 2 days after changing the password on two separate Macs.
Finally, I uninstalled then reinstalled the Safari extension and this fixed the problem.