There's defintely something new going on...I crossed at YYZ today to PHX and the lineup was about 300 ft long and cordoned off at the head. I walked passed it assuming that Nexus users could just enter, but when I got to the head of the line, I got a sense that they were only allowing a couple of flights through. (mine was one of them, so no delay experienced).

I would be some kind of upset, though, if I were denied. There's no reason a Nexus user shouldn't be able to pass through at T-2 hours and sit in the lounge...

Additional information...customs hall queue was in fact full on both sides, without about 2/3 of the lanes open. The security queue was also full. Observed at about 07:30, for a 09:15 flight.