These types of OT are very common in NCR.
Trains which leave CNB towards PRYJ between 1300hrs nd 1500hrs are controlled before PRYJ due to Maintenance Block. So if any train gets delayed then it is looped for precedence to behind trains.
12312 Kalka Mail is the most prioritized train over this CNB-DDU section at this particular time slot. From 1st June it got more slack between CNB-PRYJ so it trolls all the trains behind it but never gets looped. Everyday you will see some unusual Overtake.