After playing God of War Ragnarok for 4 hours, my FireCuda 530 starts lagging during scene transitions; why?

After jumping between the Nine Realms for a few hours, scenes that used to load instantly started hitting 2-3 second white screens, which is absolutely maddening. Monitoring showed the Seagate FireCuda 530 1TB random read latency creeping up from 0.05ms to 0.12-0.18ms on CrystalDiskMark—classic cache fragmentation killing the I/O efficiency. I tried the built-in Windows disk defrag, but doing that to an SSD is useless and just adds wear; I can't believe people still suggest that. Instead, I used the GamePP Resource Scheduler Panel to set an auto NVMe cache flush every two hours and locked the game I/O priority to maximum.