If the AI has less then 3 Magazines they will go to the next ammocrate and try to refill. As refilling does not work, they are stuck in the grab animation at the nearest ammo crate. To fix this make sure that the AI has 3 Magazines for primary and secondary weapon.

You might have to add a backpack for larger Magazines. For example for the "LMG_Mk200_ACO_F" weapon and the "200Rnd_65x39_cased_Box_Tracer" magazines.