
Source: flightradar24.com
For some unknown reason, the Boeing 777 stayed on the ground at Islamabad Airport for 4 hours 22 minutes.
Eventually, the aircraft departed from Islamabad at 5:35 PM to complete flight PK726 to Lahore where it landed at 6:10 PM. On September 10, PIA flight PK726 from Riyadh was scheduled to arrive in Lahore at 1:15 PM.

Source: flightradar24.com
Lahore Airport website shows a number of flight landings at the airport between 1:13 PM and 5:35 PM when PIA Boeing 777 flight PK726 was sitting at Islamabad Airport.

Source: lahoreairport.com.pk
Videos on social media show angry passengers inside PIA Boeing 777 flight PK726 on the ground at Islamabad Airport.

Passengers of PIA Boeing 777 Riyadh to Lahore flight PK726 selecting drinks from galley area of the aircraft sitting at Islamabad Airport.

Passengers of PIA Boeing 777 Riyadh to Lahore flight PK726 thumping cabin walls and overhead bins of the aircraft sitting at Islamabad Airport.
Abbas