Plutonium

I would like to report here my problem with BO2, when I first started the game, it worked normally, with very high fps, no problem at all. Until I opened it to play again and all of a sudden the fps dropped a lot (ps: I was with the same graphical configuration the first time I started the game, I changed nothing), but when I look up on any map, the fps goes back to normal. can you help me? thanks
My Config:
I5 6200U
8GB Ram
1TB
940M