I believe that some of the late night departures are delayed if the flying time is too short. It affects all three TW airlines, as Taipei immigration is in limited capacity in the early morning hours. They are 24/7 but staffings are possibly on the small side in the early morning hours. When I flew back to Taipei from Seattle last Sunday night, EVA Air, which was scheduled to depart at the same time as my Starlux Airlines flight, had a boarding delay due to shorter than anticipated flying time and the limited capacity of the immigration/custom facilities in Taipei.

Carfield