A new RT-AX86U image has been uploaded. As per Asus' instructions, this build does not contain the cferom component, which is what was causing the crash on certain routers versions.
Also, to be on the safe side if there are people compiling their own image, I have disabled the RT-AX86U build profile on github. People who still want to build their own RT-AX86U must do the following:
1) edit target.mak, and remove the "-disable" portion of the RT-AX86U model name
2) When flashing, flash the image that does not contain _cferom_ in the filename
This is only for the RT-AX86U (and it's variant the RT-AX86S).
Asus are still testing a permanent fix on their end.
As a side note, the RT-AX86U (and RT-AX68U) must now be built from the src-rt-5.02L.07p2axhnd/ SDK folder. I haven't received confirmation whether this was a permanent change, or if it will eventually be merged back in on top of the existing 5.02p1axhnd.675x SDK.