The aircraft returned to Islamabad because it was unable to retract landing gear after takeoff, according to news media.

Source: flightradar24.com
Around 9:43 AM, the aircraft also made a low pass at an altitude of 2,425 feet over Islamabad Airport Runway 10R/28L apparently to allow ground observers to view landing gear position and report it to cockpit crew.

Source: flightradar24.com
May 23, airblue Islamabad to Skardu flight PA251 appearing as cancelled on Islamabad Airport website. The flight was scheduled to leave Islamabad at 9:00 AM.

Source: islamabadairport.com.pk
The aircraft (AP-BNU) is still on the ground since returning to Islamabad more than 14 hours ago.
https://www.flightradar24.com/data/aircraft/ap-bnu
Islamabad International Airport runways:
Primary Runway 10R/28L
Secondary Runway 10L/28R

Abbas