Upon further research, I've found that this seems to sometimes happen to Fortnite supposedly sometimes due to updates to the game. It appears to be an issue to do with a combination of hardware/drivers and software. I'll have to look further into the issue, but I still recommend trying to figure out if your GPU or its drivers might have a fault of sorts that prevents them from running Unreal reliably. I would recommend searching up posts from people talking about such issues with Fortnite and seeing how well the fixes they share work for you here.