I updated my 2012 Mac Mini HTPC/home server from El Capitan to Sierra. Since then, I have been having trouble with the HDMI. The unit seems to be operating normally, because I have no trouble accessing file shares, Plex server etc on it. However when I try to turn on the TV and use the TV as a screen for the unit, it wont display. This is the case whether I link via my receiver as usual, or if I plug the Mini directly to the TV. Changing HDMI cables doesn't work. My Blu ray player has no problem with HDMI link when playing directly to the TV or via the receiver. Rebooting (hold the power button down on back of Mini) seems to be the only way to get the Mini to actually connect to the TV. But once I shut down the TV or change inputs, we are back to square one: the HDMI wont link and display the screen. So this seem to be strictly a HDMI freezing issue. Anyone experience this, or know of a solution?