It could be some trait trigger like the Hayasdan CTD, we don't know whether it's Hayasdan specific, culture specific or what, it's just that so far it has mainly popped up during their turn. If the same trigger affects Pahlava, it could be your problem. Could you backup your export_descr_character_traits and try using the edct_notriggers one inside the archive I posted on the Hayasdan CTD thread? Only use it to bypass a CTD though, switch back to the regular one afterwards.