During the shot when the trucks explodes from the gasoline, it is clear that "The Stranger" is not actually in the truck. The next shot has him back in the vehicle.
After the first murder victims are discovered in the trailer, the son takes the father to the crime scene where the power appears to be cut - except for a telephone answering machine that reveals the identity of the victims.
When the Mom and daughter are leaning against the van talking early in the film, the daughter is showing a white bra strap. In other scenes later when the daughter's bra strap is showing it's black, even though she never changed clothes.
Toward the end of the movie, Kinsley shoot Dollface with a shotgun. You can clearly see that Kinsley's small framed body was not thrown back from the recoil of this powerful gun.
The trailer park has plenty of trailers, and even it's own stocked shop, yet no one else wakes up, or seems to even be living there apart from the original 2 people.
When the mom is drinking wine in the beginning of the movie, she is drinking red wine yet the bottle is clear. Red wine always comes in a dark bottle.
As Kinsey is explaining the situation to the state trooper, Dollface very clearly walks into Kinsey's line of vision in the background but for some reason she still doesn't notice that she's sneaking up on them until it's too late.
When the mother and daughter are being chased into the back room by dollface the mother searches for a knife through the drawers but it's clearly visible that there is a knife sticking upside down in a jar with other utensils however it could be part of the plot being that in her panic she didn't take the time to notice the upside down knife.
The Strangers truck switches between a 1972 Ford F-series and a 1973 F-series throughout the film. Different body styles. Also, the first scene with the truck, the opposite turn signal is burnt out from that of which is burnt out later in the film.
How did Pin-Up know that Kinsey would go and hide in an industrial tube in order to scare her? She was just waiting there the whole time to pop out and frighten her as if she knew somehow that Kinsey would pick that particular place to hide in.
How did Kinsey know Luke was at the pool in order to help him and drag his body out of the water?
The gun Luke is carrying that Mike handed to him vanishes after he saves Kinsey from Dollface. He's still carrying it after they escape the trailer but it's gone by the next scene.
After Cindy helps Kinsey escape, she just stands there in the bathroom and lets Dollface stab her to death without even trying to fight back.
Why didn't the strangers think to slash the tires of the family's van? It was their only means of escape, and not tampering with it nearly jeopardized their plan to kill them all.
Mike asks Luke if he has his phone on him after finding the elderly couple's bodies. Mike collected everyone's phones and put them away earlier in the film, he should already know Luke doesn't have it.
Mike asks Luke to come with him inside the trailer to investigate the elderly couple's corpses while he sends Cindy and Kinsey back to their trailer. This is a bad idea given the situation, because if there's a group of killers on the loose then sticking together would be the best course of action, not to mention the fact that they don't have their phones on them, and Mike is disturbing a crime scene.
Dollface was waiting all by herself at the family's trailer in order to ambush them. She didn't know that only Cindy and Kinsey would come back alone, she just got lucky. Why weren't the other strangers there with her? If all 4 of them had returned, they could have easily overpowered Dollface but she didn't seem to think of this.