Why does STALKER 2 drop from 60 to 45 FPS on Sapphire RX 590?

Combat cues were missed as FPS dropped from 60 to 45. I tried lowering graphics, but the visual experience was compromised. I used the GamePP Power Plan Switcher to set High Performance and lock voltage. RTSS confirmed frame time converged to 14-16ms and HWiNFO showed 0.05V fluctuation.