Continuity mistake: When the Senator is about to be sacrificed, the cloth on her mouth immediately disappears for a split second. (01:29:35)
Revealing mistake: When they are in the hospital van, taking the senator to triage, and they receive fire from the helicopter, one announces that "Randall is dead" referring to the young man in the back of the van. It then cuts to his corpse - however, a split second before the scene changes away from his face, his eyes move towards the camera. (00:56:35)
Continuity mistake: In the scene with the shootout in the parking garage of the church, the BMW 3 Series that is used to ram the opposite car thus killing the soldiers is visible back in its original parking spot in a later scene.
Plot hole: When the security guy goes inside the secret hole, there is no way he'd have been able to cover the rug. When the other guys come in the rug is covering the hole.
Continuity mistake: When the teenage purgers get run down at the deli. The one with the Afro puffs is seen getting driven completely over and her boots appear to be knocked off her legs. The purger with the long curly is shown being knocked into and over the car covered in Christmas lights. When Lanie gets out of the van to deal with the surviving purgers, the one with Afro puffs is seen by the car covered with Christmas lights, in minor scrapes and possible injury to both legs but her boots are still on both legs. (00:53:40 - 00:54:20)