Corrupt account states when changing passwords
Proton Pass often ends up locking out some accounts.
When the user follows the Proton Pass generator UI, then Proton Pass is sometimes overly broad in which text fields it populates with the new password. The end result is a corrupted state, in which Proton Pass loses the previous password, but the account has not actually registered the new password.
This happens, for example, for forms that don't follow 100% of the most modern HTML5 designs. Usually, password reset forms provide three fields: One for the old password and two to confirm the new password. But legacy forms sometimes provide only two fields, one for the old and one for the new. In both cases, Proton Pass often ends up overwriting all of the textboxes with the new password.
When this happens, the form often fails to process, and Proton ends up erasing the current password, without applying the new one, and the user gets locked out.
Further contributing to the problem is the fact that, unlike LastPass, Proton Pass is unable to reliably save password changes after using various websites' password change form submit button.
Proton Pass has an implicit requirement to update the record before sending the form. This can furthermore conflict with any bad form validation, in the case that the newly generated password turns out not to match the website's complexity requirements.