FIDO 2 key, registered successfully with MS, that works with Google, fails on 5th char entering FIDO PIN

This question and request for help is about signing into my Microsoft Account with a FIDO 2 secure hardware device. I can sign in to my personal Microsoft account with my password. A USB YubiKey FIDO2 security key works normally for Google. Multiple times, I have registered my Yubikey with microsoft, apparently successfully (e.g., I can edit the key’s name). Upon attempting to sign-in to my MS account, On both Firefox and Edge, I select Microsoft’s security-key sign-in option, enter the correct existing FIDO2 PIN, at the fifth character of a longer FIDO 2 PIN, Microsoft immediately rejects it with the message “The PIN is incorrect.” This is the FIDO 2 PIN not a Windows Hello PIN. It happens to be digital numeric characters. I removed and re-created the Microsoft account security-key/passkey registration, then reproduced the same failure in Edge InPrivate. Please investigate the Microsoft-account/WebAuthn FIDO2 security-key enrollment and authentication path. Tag: Microsoft Account; Secure Passkey Sign-in.