FPS drops over time?

[waynelugames]

When I load up BF1 the first 1 or 2 games I average around 120 FPS on custom settings at 1080p, however an hour or so into gaming my FPS starts to dip and average around 100. I know my card isn't overheating with it running around 63*, and BF1 is well optimized. What could be the reason(s)?

CPU: Ryzen 7 1800x
GPU: MSI Radeon RX580 4GB

 

[rgd1101]

cpu temp? make and model of the psu?
ram/hdd or sdd usage?

 

[waynelugames]

cpu temp? make and model of the psu?
ram/hdd or sdd usage?

CPU temp hovers aroung 60* as well.

I have a old 500w APEX PSU that game with my system. Could it be the PSU that is causing the issue?