BPI R64 openwrt with MT7615 issue

I encounter one strange thing. use: openwrt + kernel 4.19

  1. when I first time rm overlay/* then I setting the MT7615 wireless on AC, everything good to work. but strange thing happen when I reboot the R64 device, the interface wlan1(which is create for MT7615) is not up and I need to run wifi up or /etc/init.d/network reload then we can see it up. when I connect device with it, the device will hang then reboot. I cannot get any dump log in the console.
  2. but when I only let MT7615 work in 2.4ghz, although when device reboot wlan1 still not up, but it won’t reboot after I let wlan1 up and connect to it.

how I can debug it? I cannot get any log out in console.

thanks, Water