Could it be this?
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=850221
https://superuser.com/questions/1237173/debian-computer-does-not-wake-up-monitor
http://www.thinkwiki.org/wiki/Problem_with_display_remaining_black_after_resume
http://debian.2.n7.nabble.com/Issues-resuming-from-hibernation-td4023553.html
In both Debian Stretch and Buster I've experienced the problem in the bug
report. When the system hibernates *while* the screen is locked, then upon
wake up the screen could not be unlocked. This mostly occurs at hibernation
due to idling. Timing of events is usually like, first screensaver kikcs in,
then the screen is locked, and finally system suspends or hibernates (while
the screen is locked). Upon wake up, the scxreen stays locked and it's not
possible to unlock it (otherwise the system runs perfectly - there's just no
screen)
If your problem is the same, then the solution is making sure that the screen
is unlocked while hibernating.
I don't know your power management tool and DE. In power management look for
something like,
[ ] Lock screen while hibernating
and uncheck it.
If there is an option like "Lock screen while entering/exiting screen saver"
this can be useful too. If you set it to "lock at exiting the saver", then
the system hibernates / wakes up while running screensaver (screen still not
locked), and upon wake up when you try to exit the screensaver, only at that
point screen will get locked, so you will have gone to and come back from
hibernation (via idle timeout) with an unlocked screen.
