Unhandled Server Error Has Occurred - Adding YubiKey 5 Nano for MFA

[DISREGARD: un-caffeinated moment and realized I was trying to do this from within the vault. - Mod: pls delete]

Running Bitwarden on Synology NAS via Docker. HAve had zero issues, including having Duo MFA configured and active…

Just got a new YubiKey 5 Nano and while following the posted help article for configuration:
https://help.bitwarden.com/article/setup-two-step-login-yubikey/ - each time I touch the nano I get the red popup for “Unhandled Server Error Has Occurred” - can’t save the config.

Where can I look for any relevant logging info to help troubleshoot and overcome?