I just came through a weird behaviour on the website trainline.fr.
I couldn't login unless I first clic on the password field and after that the email field. I tried to delete and save again in 1PX but same thing happened.
Also weird : I could see the form behind the login window changing when 1passwordX is filling the password.
Also weird : the web form details recorded in 1Password is full of the language possibilities offered by the website instead of the username.
Win10/Firefox 61/1PX 1.8.2
EDIT : Same behavior on macOS/Safari/1password regular extension and software
1Password Version: Not Provided
Extension Version: 1.8.2
OS Version: Not Provided
Sync Type: Not Provided