If you were paying attention, you would know that this facebook group is the BEST on keeping information clear and accurate. If I were you, I would be checking this group couple of times in a hour.
the flights between TPE/BKK and TPE/CNX both are not very profitable. There were so many costomer to begin with. Both China Airlines and EVA which operate out of TPE prefer destinations in China. In fact, out of five airlines that has flights from TPE to CNX, two went out of bussiness. It surprises me little that EVA would cancel flight out BKK once travel restriction is in place.
Also, I have a CNX to TPE ticket from EVA and I have not being able to contact them in their Taipei main office to make change.
This information is a year old: there should be a counter specifically designed for issuing re-entry permit at Chiangmai airport. After you pass the security check point, look to the left. There should be a counter that issues re-entry permit. It is before the immigration check point.
Both me an my father have used that counter many times. But it was BEFORE they remodel the area. If I were you, I would call immigration office at Chiangmai airport and ask.
And remember, because the counter is before immigration check point, I believe you can always turn around and leave.