Why does Frostpunk 2 stutter when my city population hits 2,000?

I was managing my frozen city when population hit 2,000, and suddenly the screen started twitching and freezing during map zooms. It was pure anxiety. I tried enabling High Performance mode in Windows power options, but that just cranked my fans to 2200 RPM without stopping the stutters. I then used GamePP Resource Scheduler to set the process priority to Realtime and lowered the voltage offset from 0.05V to 0.02V. Using RTSS, I saw frame times drop from 12-45ms to 16-22ms. HWMonitor confirmed the motherboard temperature stabilized at 65-68℃.