I dont know how it happens, but sometimes when fighting necros they do something that makes me unable to move or use movement skills for nearly a minute.
Its 100% sure not a condition, its definitely a bug.
I swear one time i was fighting a necro, and when he realized he was losing he just ran away right after applying this snare bug, like he purposely did it.
MARATHON CIV 5 DIFFICULTY 10 STILL GOING