Hmm, I've run into a persistent CTD at eleutheroi's turn in winter 272 BCE. Happens regardless of whether the script is activated or not, and there's never a specific action happening (no battles, no specific area centered on etc.). It feels like it just freezes up for a second, before it crashes.
This is known. Try playing with toggle_fow off and following AI movement. Yes, that takes time. Heh.