I was able to get around it, eventually. I tried running the turn without the players' turn files and it didn't crash. So then I used my opponent's file but not mine, that also didn't crash. Then tried with mine but not my opponents. That crashed again. It was something in my turn's orders that was doing it.
I also noticed that when I let the AI play my turn for me, there was a repeat of a battle from the Last turn, and the three enemy ships I had destroyed were destroyed again. I also "captured" the planet I had just captured on the previous turn. Odd.
I went in about 6 times and tried different stuff. I had retrofits, launch fighters, all kinds of builds going, some combat and ground combat, etc. It finally stopped crashing when I did everything except retrofits and launching fighters from my planets, and at that point I was too tired of replaying the same turn to worry about which one it was. That and I do software QA for a living so it was really starting to feel like work.