Linkit 7688 - sysupgrade fail if debug console disabled

I am working on a project which uses Linkit 7688 for prototype development.

Since I have a couple UART devices connected, I disable output to the debug uart.

I do it by passing boot command "loglevel=0 console=none" to kernel at booting.

However, I find that sysupgrade does no longer work, and it also reboot immediately.

If I pass "console=ttyS2,115200" to kernel on booting, sysupgrade works properly.

I wonder if someone may help me on it or give me any advise.