This is unlikely to help OP, but as this 2022 thread is now resurrected after almost 3 years, I will offer my own experience in case it is helpful to somebody else:
- You can enroll up to five fingerprints.
- The biometric user verification falls back to a regular Yubikey PIN after 3 failed attempts to match the fingerprint to one of the enrolled fingerprints.
- Fingerprint match failure is not uncommon, and happens frequently in the winter, or if you do not properly touch the fingerprint sensor and its bezel.
- While in PIN-only mode, the Yubikey will lock itself after 8 failed PIN entries (just like a regular Yubikey).
- Unlike a regular Yubikey, which can be used without a PIN if the relying party does not require User Verification, using the Yubikey Bio always requires User Verification (in the form of a fingerprint or PIN), independent of the relying party’s requirements.
If you want to not have to worry about unauthorized use of the Yubikey (if lost, stolen, or accessed by someone else), then you need to set a sufficiently strong PIN.