xset -dpms (turns off display power management) and xset s X X (replace X with the time in seconds after which you want the screen to go blank). It's just an idea but i think DPMS might be the culprit and disabling it would at least work around the problem while the screen blanking configured by the xset s command would act as a replacement (which doesn't actually save power but looks the same). If that leads to an acceptable solution those settings can also be put into your X configuration so you don't have to set them again every time you restart your system.Do you mean the state where the monitor gets turned off? If this is the case it might be worth to experiment withxset -dpms(turns off display power management) andxset s X X(replace X with the time in seconds after which you want the screen to go blank). It's just an idea but i think DPMS might be the culprit and disabling it would at least work around the problem while the screen blanking configured by thexset scommand would act as a replacement (which doesn't actually save power but looks the same). If that leads to an acceptable solution those settings can also be put into your X configuration so you don't have to set them again every time you restart your system.
xset s off and just use a screensaver but i don't think it will make a difference. To me it looks like system is going into some kind of standby mode but not coming back afterwards but i wouldn't know how to diagnose that. Maybe you could try something radical like disabling ACPI just to see if that makes a difference. https://www.freebsd.org/doc/handbook/acpi-overview.html has a part about disabling ACPI. It also says to rather use APM for old systems. Maybe that's worth trying.I see. I guess you could turn off blanking completely withxset s offand just use a screensaver but i don't think it will make a difference. To me it looks like system is going into some kind of standby mode but not coming back afterwards but i wouldn't know how to diagnose that. Maybe you could try something radical like disabling ACPI just to see if that makes a difference. https://www.freebsd.org/doc/handbook/acpi-overview.html has a part about disabling ACPI. It also says to rather use APM for old systems. Maybe that's worth trying.
The funny thing is that it happens with the Xfce desktop environment or the system in terminal mode before entering the Xorg graphic mode, which can be? I added Mate's graphical environment and it works well.
The problem happen with light desktop environment like Xfce, or on the base system terminated in terminal without entering Xorg or light desktop environment like Xfce. With "mate" desktop environment works well, there is no such black screen blackout as happens with Xfce or base system terminated in terminal.What about disable any screensavers software, e.g: xscreensaver, xfce4-screensaver? Also have a look at XFCE's power management setting.