I recently started having an issue on my file server where the monitors are coming out of sleep overnight. They go into (and stay) in a state where the screen is black but the mouse cursor is visible and so the monitors are "on". This is basically the same state that you would expect them to be in right before the screens go into power saving mode.
The screens correctly turn off when inactive for 10 minutes and they correctly turn on for mouse or keyboard input but I have not been able to figure out why they are entering this black but powered on state when left unattended for longer periods. I don't believe it's a spurious input because they would go back into a sleep state on their own if that were the case.
I'm using Ubuntu 16.04 with NVidia card and drivers. The issue was occurring with the original 384 drivers and it is still happening when switching to the older 340 version. I've been using 16.04 on this machine for several years and haven't had this issue until recently.
I've checked the syslog but don't see anything suspicious. Any thoughts on what else to check would be appreciated.