After I lock my system and my screen goes off (black), it doesn't wake up anymore. As soon as that happens, I have to use my power button to reboot the system, else I will not be able to login.
I tried disabling USB auto suspend, as suggested over here: Ubuntu 14.04 doesn't wake up after screen is locked and blank which did not work for me, unfortunately.
For now I have set the "Turn screen off when inactive for:" to "Never", via All Settings -> Brightness & Lock. Hopefully that will fix it for now, but if anyone knows a proper solution, please let me know :)
EDIT: Setting "Turn screen off when inactive for:" to "Never", does not work! After locking my system, the screen will turn black anyway and I'll unable to login again.
EDIT:
Alright, so xscreensaver seems to be the solution for now. But you have to make sure you set "Blank After" (through the settings of xscreensaver) to a couple of hours or something, because as soon as it goes "Blank", the same issue occurs. I've set it to 600 minutes for now, because I always shutdown my pc after work, but I have to make sure it keeps working while I'm at work so I don't have to force restart it after a meeting for example.
sudo apt install xscreensaver), given on bugs.launchpad.net, solves the problem! – Erik van de Ven Dec 06 '17 at 12:28