I recently bought Pixel 4a as a replacement for my Pixel 3a, and after restoring the content from the old phone, I encounter following issue with Enpass.
I'm using biometrics (fingerprint) as a identification method, and now on Pixel 4a, after every fingerprint prompt, I also need to enter Master password. On previous Pixel 3a, the behavior is expected one, with fingerprint check, the Enpass is unlocked without password prompt.
I did manage to notice, that when I enable the Biometrics option in the Settings, and authenticate myself with fingerprint, I'll get the following toast message at the bottom of the screen: "Failed to encrypt the data with the generated key error". Biometrics seems to be enabled then anyway (it's checked in Settings), but when I want to open the Enpass to get the password for any app/webpage, I need to also enter my Master password, as mentioned previously.
As for a troubleshooting steps, I tried Erase everything option from Settings, as well as reinstall Enpass app.
I'm currently using Enpass version 18.104.22.1680 on a Pixel 4a with latest Android 11 (June 2021 security patches).