It was showing a big delay earlier on the arrivals board so I suspect they cancelled due to it being due to depart during the stupid night curfew that was put in place as a condition of the runway extension many years ago.
PIA have fallen foul of it many times and have promised to put a quiter aircraft on the route (B777) but still use the A310. LBA still hasn't seen a 777 so I doubt they ever will mainly due to runway length.
It is known that PIA tried to pull the route back to MAN last year but were persuaded to stay by a councilor who used to work in the travel industry. It is clear that the route is viable with the large Pakastani community in Bradford, but it doesn't make sense to PIA to operate from both LBA and MAN. They even stated that the trip across to MAN wouldn't be too much of an incovenience for the Yorkshire pax.
The only danger is that if they do pull the route back, the travel agent that started the flights with Shaheen may ask them back now they have a 767 and 2 A330s, and if they upped the flights again back to 3 weekly PIAs MAN operation would certainly suffer.