Err... Asuswrt-Merlin's team consists of one single person - me.
What I'm saying is that Asus has made some changes in newer firmwares, you will have to wait for that code to be implemented in an Asuswrt-Merlin release in the future.
It looks like asus released a beta 380 based firmware for the AC66R. Firmware version 9.0.0.4.380.2695 ... I am guessing this is newer than the 380_1354 you built 380.58 on right?
Question, you base the firmware off the standard GPL release, does that include updates like this or do you have to build each model off of the specific firmware version for that router.