I don't feel comfortable stating any details here (I know this doesn't help) but on my bank website, there's 2 fields 1 for username and the other for description + the password field. In macOS and Windows the username get filled correctly but not using the Linux Beta, the username get filled in the description field.
I can provide more details in private.
1Password Version: Not Provided
Extension Version: 0.8.4
OS Version: Ubuntu 16.04
Sync Type: Family