I recommend the usual suspects be examined first:
- Check for memory leaks
- reinstall gdm (
sudo apt install --reinstall zorin-os-desktop gdm) - Check your graphics- Are you using AMD? Nvidia? We may need to try different drivers. The more information you include, the more we know and can off tips.
Many users have reported that on Zorin OS 17, the computer will put itself to sleep at a specific time, then not wake and will instead seem to crash and close all their apps requiring a hard restart or re-login fresh. You may be afflicted by this, as well.