Exactly. Fast track works very well at GOT in my opinion. One has to keep to the right at the TV screens and in my experience twice in 20 odd trips remind the personel regarding entitlement. Walk straight into the dedicated area in the morning or it cuts straight to the front of the normal queue during the day as per alibi.
Sounds like you maybe missed keeping to the right and ended in the normal queue, well mistake on the person scanning, although they typically do not argue if fast track entitled people want to go in the normal lane.
During the mornings when security stretches to the stairs, I and many others walk past the gaggles straight to the Fast Track entrance. Never had anybody complain, maybe people thought you were not entitled and just simply jumping queue.
My only complaint is that LH does not pay for Fast Track at GOT. Admittedly if they paid for all *G then Fast Track qould not be fast at all but given how much LH charges for C, one would expect Fast Track.