This infinity loop bug in AI turns is also happening on other mods.
In pie's Ancient Europe mod for example, or in Xyth's History Rewritten.
AFAIK it wasn't solved, at least not perfectly, but in both cases it was connected to pirates, or some sort of AI pirating feature
EDIT: Apparently Xyth knows more about this topic:
http://forums.civfanatics.com/showpost.php?p=13112876&postcount=39
"It's caused by a unit getting stuck in an endless loop of joining and splitting from a group. At this time the only solution is to go into worldbuilder and delete different units until you find the culprit. Most common triggers are naval units passing through other naval units (especially Pirates/Privateers)."