CPU and GPU usage drop along with FPS drop in Fortnite

[Masternewbz]

Problem : After playing Fortnite for about 1 hour and a half, my CPU usage drops from about 20% to 11% ,GPU usage from 45% to 25%, causing FPS to drop from 200-350 to 120-180.

 

System specs :

Prime deluxe x299
i9 7900x @ 4.2 Ghz
4x8 gb 3200 MHZ corsair vengeance lpx XPM profile enabled
1080 gtx ti aorus xtreme 
850W power suply EVGA gold.
H115i pro

 

Power plans are all on maximum performance. Temperatures are stable at CPU 45 degrees and GPU at 65 degrees.

 

After I restart the game, immediatly it comes back to normal and it takes awhile for the problem to start again.

 

What could be causing this CPU and GPU usage ? Why restarting the game is fixing it temporarily ?

[Masternewbz]

Anyone ? Could it be a Memory RAM issue ? maybe overheating?