Why does Space Marine 2 stutter on Manli RTX 5080?

I felt the immersion break as frame intervals jumped from 8ms to 22ms. I tried reseating the GPU, but the system black-screened. I enabled the GamePP Resource Scheduler, set priority to Real-time, and switched to High Performance. AIDA64 confirmed VRAM temperature stabilized at 58-65℃ and bandwidth hit 62%.