Unless a manufacturing fault is discovered, we will never know what the cause is. Vettel said there wasn't anything unusual at T1 when he inspected it after the race, the engineers haven't been able to figure anything out. The only thing left is Pirelli's forensic analysis of the offending tyre and its debris.
I don't like two-stage kerbs (used here and India). The flat portion invites overuse, and the high-angle portion poses too much risk of physical damage to the car.