Quoting myself just to show what Iīm referring to
Iīm a total noob at this - so I do not know how to check - BUT can there be something with MIMO settings for the antenna?
in the nvram you can change:
wl_mimo_preamble=mm
wl0_mimo_preamble=mm
(standard)
moreover you can do some advanced settings with the wl command. (see attachment)
I don't know much about this, so you can break it, or you can make it