Frank gets impaled just above his knee with a wooden stake. Once the stake is removed and the leg bandaged, he walks with only a minor limp and even outright runs at points, when his leg would be incapable of supporting his weight at all.
Sammy watches the Woody Woodpecker cartoon, Pantry Panic (1941) in her room, and judging by the audio, the cartoon order seemingly jumps around at random.
Unless Abigail had recently gone on a murder binge of truly epic proportions, it would be impossible for all the dozens of bodies at the pool that Sammy falls into, to be all so fresh, and for all of them to be seemingly in the same state of decomposition specifically if they have been sitting in a pool of water. However since Lambert was also at the house and it appears that the property has some history for Lazar, it may be that they and other vampires use that house as a "dumping ground" for other bodies, rather than leaving the bodies where they died and risking attracting attention. It could also be that the draining process gives some vampiric properties to their blood which acts as preservation but not enough to turn them.
When Abigail is loaded into the van after being kidnapped and drugged, Joey checks her pulse, as Abigail is a vampire, and therefore deceased, there would not have been any pulse. However there are other vampire myths that are shown to be false, like the effectiveness of garlic and crosses, so it could very well be that this was a myth in their version of vampires as well.
Lambert collects seven cell phones into a bag, but when Joey takes hers from the bag it seems that it's the only one. Actually hers is just the one on top; the back cameras of at least another cell phone can be clearly seen.
When Frank cleans his glasses after killing Lambert, a large drop of blood trickles up the wall next to Joey, revealing a reversed shot.
The crew goes to the mansion from which they kidnap Abigail with two cars, a black SUV and a van. They all leave in the van and leave the SUV behind. This doesn't add up with Lambert's extremely cautious planning.