I’m not quite sure whether I correctly understand what your meanting or not, but I’ll try to figure out a solution.
You meant that you swich your monitor to TV channel first, then back to HDMI/Khadas, the Ethernet of VIM2 will turns off, right?
You tried with two different ROMs with same issues, right?
What do you mean that disconnect the board? Plug out the USB-C power cable and plug in again?
Is it possiable for you to recoard a simple video, it will be helpful