It could be your graphic card, its settings, although the flaw should act every time. Seems like it is some harassing program working with a certain pace = some update / upgrade program? Check what you have running at startup, a place could be here: Link Removed
You have some program looking for updates "every three days" or something? Font related? Screen related? It could be as innocent as a game?
It must be something like that, a bad mushroom.
We also recently had a problem with a missing font. I do suggest that you make a thorough scan with your Antivirus, and perhaps Malwarebytes. It may be you have a boogie.