Hey there. I'm happy to know you figured it out, glad to hear it's working now.
I wanted to suggest reinstalling the game; I had this problem with some Steam games and it worked, but after you shared that it might have been your GPU, I realized this is indeed the closer reason.
Disabling the GPU and reinstalling it probably prompted the drivers to be updated, which might have needed updating.
GL&HV with Fortnite!