That's odd. I've used London Blackfriars semi-regularly over the last 18
months (including earlier this week) and as a Y-P ticket holder I've
never had any problems with the gates.

May I ask from where you usually buy your tickets?

Luton Airport Parkway.

And as of last week, I still can't get through the gates - yet other gates
let them through fine. (Including Blackfriars LUL).