Why is the Civilization VII interface frozen during turn transitions?

In the late game, clicking 'End Turn' leaves the interface frozen for 5 seconds, which is absolute agony in a strategy game. I tried disabling all unnecessary background services, which freed 2GB of RAM but did absolutely nothing for the turn-switch lag. I then used the GamePP Resource Scheduler to set the game process to Realtime priority and boosted AI computation threads to High. RTSS showed frame times dropped from 40-120ms to 15-25ms, while AIDA64 confirmed CPU temperatures stayed at 78-84℃ and CPU-Z showed 3.6-4.2GHz.