I could not update my TM-AC1900 (TMO's version of the Asus RT-AC68U) from asuswrt-merlin FW version 380.61 to 380.62 or 380.63. I have been installing periodic merlin FW updates for 2 years! Somehow the CFE blacklisted non-TMO FW!
Here are the details of how I fixed the issue. Thought I would...