I have the 4k stick in hdmi2. I put source to tv and watch my basic cable, i change source to hdmi2 and it is not detected. had to unplug from outlet. happens every now and then. had no problem with my other roku stick on the same tv.
First, try pressing Home on your Roku remote a few times after you switch to HDMI2. Second, look for a new "power saving" option under Settings->System->Power.