Just to chime in, I’m experiencing a similar problem since the last update. I’m running KDE with an Nvidia GeForce GT 1030 connected via display port. After some time of inactivity my screen turns itself off, but since the update I can’t wake it anymore. I can manually turn the screen back on, but it stays black. There is no reaction to either mouse movement or keypresses.
I have hibernate turned off and from the outside it looks like the machine is staying on, it just doesn’t wake the screen anymore. (I might add, that I’ve a second GPU installed, that is reserved for a VM, so this might complicate things.)
It sounds like a different issue, so I’ve moved it to a new thread.
EDIT:
Could you please give some more information.
What are your settings:
System Settings → Energy Saving
Specifically:
Suspend Session → After a period of inactivity
Display and Brightness
Does it wake up ok if the monitor has only just turned off?
If so, roughly how long does it take to become problematic?
Could it be trying to sleep but not succeeding? If so, have you tried preserving video memory (as in the other thread)?