I mirror, one set has HDMI the other cables. I was having the issue with the cable connected TV, I had not yet checked the 2nd TV because ( the HBO On Demand) menu issue (mentioned earlier) in the other Hopper suckered me.
I finally went upstairs and checked the other TV. Turned it on and it was in standby mode, since I was mirroring that should not have been the case because the other TV and it's Hopper were on. I hit Hopper power on the remote and the channel I was getting the message on downstairs miraculously appeared upstairs...checked the TV that started the whole mess (down stairs) and all was well.
Often it is the sign of a bad HDMI cable or connecter, I suspect it will happen again and if it does I will replace the suspected cable.
Thanks for asking, Charlie