When Cole is fighting Max, he uses Allison's chopped off leg as a bludgeoning weapon. Shortly after, Allison's body is seen, still having both legs attached.
Deacon scratches his left ear with his left hand (his thumb is back) then with his right hand in the next shot at 38 min.
It's impossible to drive a Nissan Leaf EV while a charger is attached. The on-board software will not engage the drive wheels or allow the vehicle to enter drive mode.
The vehicle owned by the guy playing banjo by the fire is a Subaru outback XT, no doubt chosen for it's functional hood scope so Sonya would have something to hold onto while they spun around. However all Subaru's have symmetrical all-wheel-drive, and would not have been stuck with one wheel lifted by the rock.
At the gas station where Cole's father is recharging the car, Cole awakes in the passenger seat and his father asks him to unlock the car doors. Why would he have locked the car if he did not take the keys with him?
Urine is not sterile.
The long needle is drawn at random in the forearm at a 45 degree angle. This means that the muscle or tendons are punctured but blood cannot be drawn from such a prick.
Phoebe boards the houseboat to ask for gas, saying her jet ski is low. Then she and Cole proceed to use the jet ski for escape, leaking gas behind them, and still manage to make it to Phoebe's destination.
EDIT: Running could have just as easily meant that she wouldn't have enough to make it back after her trip, not that she didn't have enough to get there. It could have also been a random made up excuse to explain why she's there.
When the giant boulder crushes Allison's body, blood splatters onto Cole and Phoebe, yet neither of them get red, revealing it is obviously CGI.
Obvious fake left arm (revealed by the plastic hand hanging at the end of a thin straight prosthetic arm) cut off by the machete.
The first shot of the house is obviously stock footage from the first movie, even though the house was destroyed between the two movies.
In the first movie, Cole is 12 years old. This film takes place two years later, which would mean Cole is 14. Yet his character is a junior in high school. In the U.S., a typical junior is at least 16 years old before they start their junior year.
When police office is questioning Cole's parents, his badge says "Illinois Police," assuming the setting is somewhere in Illinois. However the lake scene is obviously in Southwest Canyon country, like Lake Mead or Lake Powell. There are no such desert/canyons near Illinois.
The two protagonist did not turn the boat lights off (or let if float away) so as to better hide their location.