This could also be caused by naval units, I believe, most likely Privateers or similar pirate units. Keep an eye on the thread Leoreth just made here, or have a look around in his modmod's subforum (Rise and Fall of Civilization: Dawn of Mankind), where people discussed it as well sometime ago. I believe they found that another mod had tried to fix this bug as well, but failed, or something like that. I don't quite remember, but it's a lead at any rate. However, if this is what causes your infinite turn, then I believe there is no official fix that prevents it from ever happening (you can sidestep it by reloading an older save and deleting the unit that is causing it, but...).