I've experienced this on a handful of pages, one reliably reproducible one is https://console.aws.amazon.com
Clicking on Autofill for the relevant login, appears to make use of the account2 and username2 web form details the first try. Clicking on Autofill a second time will use the correct account and username web form details.
As mentioned in the previous discussion, modifying/removing the web form details is not possible on 1PasswordX.
1Password Version: Not Provided
Extension Version: 1.17.0
OS Version: Linux (Firefox)
Sync Type: Not Provided