Black screen appears a few minutes after boot

I have LXDE running with the autostart … but If I try to have a remote connection via VNC 10 or 15 minutes after the Boot
I can run the remote connection but the screen stays BLACK !!!

It is exactly the same situation when I connect a screen via HDMI on the Sparky … the screen remains Black
I need to reboot and establish my VNC remote connection or connect the Screen immediatly, in order to have
the screen prompting correctly

DietPi version is 6.1