Plot hole: Gerry's wife uses a rocket boot to break through a window and then slides down a curved wall to get to their son. She does so gracefully and takes off running. Gerry slides and takes a hard tumble and rolls down, landing on the ground. The next shot shows Gerry running behind his wife and not too far away as they reach their son. Even if it was to show a little time passing, there was not enough distance between where they broke the window and their son for Gerry to have picked himself up and catch up to his wife before reaching their son, especially with his wife being a worried mom doing a full on sprint to her kid.
Plot hole: When Grug is trying to escape from the explosion behind him he sees Douglas and says "Douglas! Hey I know that guy!" This is not possible since he neither knew the name of the creature or was nowhere around when Douglas was with Thunk.
Suggested correction: Thunk might have told him who Douglas is.
Plot hole: During the final scare event, Mike gets a perfect score because Sully broke the simulator to allow the 6th scarer to get a perfect score no matter what. After the contest, the simulation resets and Mike pretends to scare the child in the simulator and it registers a perfect score on the scoreboard for the 6th scarer when it should really have registered a score for the 1st scarer, because the simulator had been reset.
Plot hole: If Chester's plan was to steal the machine the entire time why didn't he just have his people steal the machine while it was still floating in the air during the first film? There was plenty of time to capture it before the food started mutating so what was he waiting for if he needed it so bad?
Suggested correction: Because he wasn't there in the first film? He first made an appearance in this film, doesn't know how to work the machine without Flint, and how the hell would he even get it in the sky? He also didn't even know about it, or what happened to Chew and Swallow, again, until he made an appearance in this film. Not a mistake.
Plot hole: Emily begins to pull Henry out of the shed, but however there is no track leading to the other end. Also, the turntable is not big enough for both engines to fit on.