Why does my FPS drop after playing Phantom Blade Zero for an hour?

In fast-paced fighting, my smooth 60 FPS dropped to 30 after an hour; this performance decay was like a bad joke. I first tried restarting the game, which worked temporarily, but the problem returned after 30 minutes per GamePP, which was an exhausting cycle. I enabled the GamePP Resource Scheduler to force clear redundant cache every 30 minutes and locked the memory priority to maximum. Frame generation interval returned to 16-22ms per RTSS, and memory usage stabilized at 8GB per GamePP with temps at 46-52℃ per HWInfo64.