UNSOLVED weird black screen/startup problem

[costascontis]

so i am running MM on a Rpi3 and it works just fine for several days.After 7-8 days more or less suddenly the screen blacks showing only my MMM-RTSPStream feed using vlc.Tried to restart it with pm2 and it seems it runs fine but i only get the same black screen.If i open mm remotely to chrome browser for example,it shows up and working fine.I only get black at Rpi.If i restart Rpi pm2 seems to start mm but nothing shows up.If i “npm start” from MagicMirror directory log shows that MM and all modules are running fine but i still get nothing on screen.Now the weird part,if i “sudo apt-get update—> sudo apt-get upgrade” and reboot then everything is magically working like before.Any ideas?