That's because the XBox can't handle all those animations at once. Although, if you're looking for a strategy to get around laying a bunch of mines, try switching on stealth, going right up to the Vulkar lieutenant and planting a devastating mine at his feet. Then go into solo mode and have a fully upgraded weapon equiped. Place Mission and Carth at the entrance to the room, then with your PC place another mine at the entrance to the room and attack the Vulkar lieutenant from behind. After this, run out of the door towards the mine. Their numbers should have been thinned by this. However, make sure to kill the lieutenant first. Just make sure to plant the mines far apart. Another option is to hack the computer terminal near the armory so you don't have to get the keycard from the lieutenant and avoid the situation altogether.
"No, Mama. You can bet your sweet ass and half a titty whoever put that hit on you already got the cops in their back pocket." ~Black Dynamite