I received an email today (14th 17:25) that my flight tomorrow (15th 13:10) will be delayed by 2 hours, and advised that I could checkin etc as per normal. The email was auto-generated rather than from the local TG office.

I suspect that B787-9 HS-TWB is out of service for some reason. This aircraft would have been scheduled on a normal rotation. Instead HS-TWA will be turned around from its present AKL-BKK sector, and depart 2 hours later than usual for TG491 to fly BKK-AKL.

I know THAI is not perfect, but this example shows that indeed THAI does have appropriate systems for advising pax of changes. Any system can become overwhelmed by the unforeseen...