I use a MacBook Pro (prev gen) connected to a Cinema Display, PSU, keyboard and mouse. Prior to High Sierra, everything worked fine and I could run the MacBook Pro with the lid closed.
After High Sierra, with the lid closed, it crashes 2 - 4 times a day. Completely freeze except my music stream continues. When I reboot, again with the lid closed, I don't even get a log in screen. For this to show up, I need to open the lid and reboot from the built in keyboard, then it works.
When I have the lid open all day, and screen mirroring, it crashes a lot less, maybe every second day. But, I also get all sorts weird display issues. Some apps more than other. Safari and Slack being the apps with the most problem. Restarting the app does not help. Need to reboot.
So I guess there must be bugs in the display drivers. Very frustrating. Hope Apple get us a quick update that fixes these problems.