I tried to install new firmware by using sysupgrade -F through ssh.
It worked but wifi was not working.
Then I flashed back stock firmware, and tried doing the clean flash as in the instruction.
That makes the router went into bootloop, after loading kernel.
I restored it using TFTP and serial console.
Does anyone tried last build (from December 2018) downloaded from mega.nz?
Is it working on your routers?
Do I need to do anything special to avoid bootloop?
Now I flashed success some previous build from July 2018 which I had on router before.
It works OK, but sometimes 2.4GHz WiFi hangs.