So I was able to get the game to crash! But I don't think it has anything to do with AI behavior--but maybe with quantity of AI CPU usage.
First, I was playing on a small map against three opponents.
The game first crashed at about the 175 turn mark when there were about 65 ships (in two stacks) next to the planet I quarantined.
I loaded the autosave and had one of my units attack the AI for the first time then move back into the blockade. I hit turn, and the game crashed to the desktop again.
Next I had my unit attack theirs and then moved the entire blockade from the planet. Crashed.
So I backed up the game to a previous save (only about 5 turns), removed the blockade, and proceeded. The planet was colonized (all planets were now occupied) and the game didn't crash. I moved my units out of sight and everything ran okay for a handful of turns (got to about 180). Then I moved my units back into sensor range of the ship stacks, and the instant they did (during a turn/auto-move), the game crashed to the desktop.
I also played with what I could see on the screen (zooming in very close to an unoccupied area of the galaxy), but the crash still occurred.
As I mentioned previously, this did not happen on a 1v1 tiny map, but I'm unsure of whether this is related to the map size or the number of players, both, or neither.