UPDATE: Possibly Solved. . . Replaced SSD.
I upgraded my Mac Pro to High Sierra. For the most part it was seamless. The installer automatically migrated the HFS+ file system to AFPS and everything appeared to be working great. As it turns out. . . I have a new intermittent problem that causes the computer to become unresponsive while idle.
It presents primarily as a failure to wake from sleep (backlit black screens instead). Display sleep is actually all that is required to present and of course it is not every time. It is often enough for me to return to the 90s habit of shutting down my computer after I finish using it lest I cause irreparable harm to my mounted file systems. Here are some things i have discovered while trying to resolve. Sometimes i can access the computer remotely, other times not, never graphically. Sometimes the system hangs as soon as it goes idle, sometimes it continues to operate. Sometimes it restarts from “sudo reboot” from an ssh session, other times it just hangs completely when i try. The console logs are useless. Nothing at all before the reboot. When unresponsive, there is nothing to do but hold the power button.
The difficulty i am having at discovering the core of the issue combined with the fact that my remote backup has gotten stale is driving me crazy. There seems to be people complaining about this on every Apple forum there is. I am not alone: