I see this message in your log file:
So the obvious question is have you modified the bootloader? Is the router a genuine RT-AC68U or a modified TMobile device?Code:May 5 13:05:09 wanduck: WARNING - router is in manufacturing mode, and can behave unexpectedly (did you mess with your bootloader?)
This unit was given to me from the US, and already have the ASUSWRT-Merlin firmware. I checked the front and there's both ASUS and T-Mobile name, which means it's a modified device.
I'll try to search and buy a second-hand genuine RT-AC68U and start all over again, as this changed bootloader could cause this issue.
Thanks for finding the problem, and thanks also to everybody else for pitching in.