Autofill issue with Vanguard website?

This problem started a couple of months ago and there has been at least 1 system update, at least 1 update to 1Password and several system restarts during this time. So, yes, I have completely restarted 1Password though not explicitly via the menubar method mentioned above. I've also created a new login and that does not fix the problem.

Just to be clear, the user name and password fields are being filled by 1Password. I can even display the password in cleartext by clicking on the eye icon next next to the password field. However, nothing happens when I click the "Log In" button.

This problem also occurs with 1Password on iPadOS and the built-in browser.