Why does my MSI B450M slow down in Rainbow Six Siege?

Write speeds dropped from 5000MB/s to 600MB/s. I tried changing virtual memory, but it worsened conflicts. Using GamePP NVMe Queue Config, I increased queue depth from 1024 to 2048. CrystalDiskMark now shows 65-70MB/s 4K reads and 4s load times, with 45-52°C disk temps.