It is related to sleep, I think. To clarify, I keep my MBP closed in a vertical stand 100% of the time and use it via an external monitor. When I attempt to use it in the morning or after returning to it after it has slept, it sometimes will not turn on the external monitor when I click the mouse or tap the keyboard. At this point, it will still be working and not have crashed yet, so I can open the lid and use it via the built-in screen. Then I have to try and unplug and re-plug in the external monitor to get the external monitor to turn on. About 90% of the time when I do this, the external monitor is recognized and I can close the MBP and go back to using it exclusively via the external monitor and apple bluetooth keyboard/mouse. The other 10%, immediately when the external monitor is reconnected, I hear the fan suddenly go to full blast for about a second and then the machine switches off. Btw the external monitor is an LG 31MU97 4K connected via a USB-C -> Displayport cable. The 3 things connected to the MBP are the monitor, the belkin ethernet dongle and the apple power adaptor. I'd previously been using this same monitor with my old 2013 rMBP for two years without any such issues.