For me the last release is bad in 5Ghz with Xiaomi Router 3G and also with a WR1200JS.
I have find in my linux computer an old release ( 4.14.102 )
Xiaomi Wifi Router 3G - 18.06.x / Wifi issues 2.4GHz + 5GHz
I just restart a compilation and the firmware 4.14.102 will be ready in less than an hour
https://mega.nz/#!PkcTwSCI!ci8OHXkLhDH-oNExHDrKNG2qTFouPROfJvTorx8c3GI