Why does PUBG drop to 120 FPS on Valkyrie V360 MIST?

I was cautious about the frame drop from 144 to 120 FPS in PUBG. I tried 100% fan speed, but it made the system unstable. Using GamePP Power Plan Switcher, I set High Performance and adjusted the fan curve to 85% at 78℃. HWiNFO shows temps at 75-78℃. Fraps confirms 140-144 FPS. The performance is verified.