This happened on turo.com's login, which is a pop-up panel. The 1P icon appeared in the username field. Clicking it popped up the appropriate 1P login info banner. Clicking the banner to autofill had no effect whatsoever.
1Password Version: 1Password for Mac 8.2.2 80202080 on BETA channel
Extension Version: 1Password for Safari 2.1.2
OS Version: 12.0 Beta (21A5534d)