sfx2000
Part of the Furniture
FA is not supported in recent firmware releases for the RT-AC88U, due to the switch to GMAC3 (don't ask me what it does, I have absolutely no idea, I only know it's related to how the wifi and Ethernet switch talk to one another).
GMAC3 is blackbox inside the switching fabric of the SoC I'm told... the demands on this class of SoC are pretty high with 5 gigabit ports, up to 3 11ac 4*4:4 radios (the AC5300 class), and in the case of the AC88U, a discrete external switch with four more downstream ports...