Cubase Freezes after leaving it open for a long time

A couple times I will have a project, and keep it open for a few hours while I leave for an errand. After I return I can’t use Cubase, it appears to be hanging, and I need to restart it.

Not sure why this is happening

Mac or Windows ?
If Windows check the advanced power settings, and make sure USB is not allowed to turn off to save power.

Do you mean restart Cubase only, or restart the computer?