One time the game screwed me on a checkpoint in the second level on legendary. I had just lost both of my marines (gunner and man in side-seat) and my shields were down. I was about to revert to the last checkpoint but then I got a new checkpoint right at that moment.

I was like ten feet away from the jeep with two elites running towards me in the front and a grunt coming at me from behind. It took me a few tries, but I got in the jeep and took em all out with two life marks left.