As the title states, I often CANNOT kill an enemy by ramming them, and the usual end result of ramming them is that they just simply either get pushed out of the way or they stay stuck to the front of the Ghost. This is extremely frustrating because I am trying to speedrun the campaign on Legendary, and with the Ghost not being able to kill anyone, it is REALLY making life difficult.
Does this happen immediately after a checkpoint? I know in Reach at the very least enemies have ~3 seconds of invulnerability to splatters and possibly other types of damage when hitting a checkpoint.