Why does Expeditions: Rome stutter when loading battles?

Loading Rome city scenes often hit a 0.4s absolute standstill, which totally disrupts the strategic rhythm. I first tried cranking all graphics options to maximum, but that counter-intuitively made the driver latency worse. I then ran the GamePP Peripheral Driver Conflict Detection Tool, found a conflict between the NVMe and an old chipset driver, and updated them. RivaTuner showed frame generation time stabilizing from 14-42ms to 11-16ms, I/O wait hit 18-32ms via AIDA64, and temps stayed 48-55℃ per HWiNFO.