It's not usual, it does happen sometimes. Probably around 1 in 20 of mine are B gates.

For domestic departures (and DUB & JER), gates fitted with the facial recognition equipment are A1-A3, A5-A9, A11-A23. My experience is most are these A gates but often spread right across the range.

Bus gate A4 (which is divided in to A4a and A4b sub gates) is a dedicated UK/DUB bus gate, and as of early 2018 A10a has also been fitted with the facial recognition equipment so can also be used as a UK/DUB bus gate.

Also two B gates (B44 & B45) were fitted with biometrics since around 2020, so it is possible you could even go from T5B.