Sudden FPS drop after 1 hour of play or sometimes even less (PC).

Overheating, memory leak, nothing else comes to mind.

You can do a RAM, CPU and GPU stress tests to see if hardware is an issue. [Need 3rd party programs to do those and some time]

Also check if all CPU cores work on the process ( If you get 90% for the first hour and when FPS drops it's 75 or 50).

Also disable origin in-game overlay. You don't need it, compared to Steam's it's un-usable anyway. People report up to 20 fps drops with it on.