I ran 6.8.3 with never any problem for over a year.
After the upgrade to 6.9.0 that went very smoothly it ran for at least a day without issues.
For the past two nights the system was online but sometime overnight when I come back in the morning I return to a system that is either "powered off" (no sound or anything) or the screen become black, no reaction on keyboard presses and can ping but no responses on the network by http, telnet or ssh
I left a monitor, USB keyboard and mouse plugged to the server but this morning it appeared to be off again.
1) its plugged into a UPS for reliable power.
2) no other unit in the house has had any power related event for the entire week.
3) unit boots after I push the power button.
4) manually set static IP responds to ping but not to http, ssh or telnet.
5) only way to restore it is to hard power the unit off and cold boot it.
DELL PRECISION T5600
BIOS: A19 (latest release - Aug 2019)
CPU: Dual xeon
RAM: 112 GB
GPU: NVIDIA Quadro P2000