I have had two monitors for my Late 2016 MacBook Pro running the latest updates, a 1080p one and now a 4K monitor. Both have had the same issue described below.
When I connect my external monitor to my laptop (using HDMI to USB-C) the monitor is turned off, however, it is detected as I can move my cursor onto the other screen (though I can't see the cursor as the monitor is turned off). When I turn the monitor on it does not display my other screen as it should but turns itself off again. This cycle of me turning the monitor on and then it turning itself off happens about 5 times until seemingly randomly it displays as it should my desktop background and any windows I have open.
On further experimentation if I plug a USB-C hub into my laptop and then connect an HDMI cable from the hub to my external monitor the problem does not occur at all.
This is becoming very frustrating and I can't seem to solve the issue. Any help would be greatly appreciated.