I was there last night, approx 7:30p, YVR-bound. The upstairs lines were all long, so I took the staircase down.

There was a GTAA employee (judging by the burgundy sweater/vest) challenging people for cards/BPs, but after me, she took the next two travellers from the other (non-priority) lane, and moved them to the end of our line.

My guess is it's the GTAA's responsibility.