When Norman is speaking to Coach Bishop by the truck before going inside the school to get the basketballs then comes back outside minutes later to find Coach Bishop dead, the weather is clear. When Coach Bishop's murder is shown in flashbacks, it takes place in a heavy, wet snowstorm.
Throughout the movie, scenes of there being a few inches of snow on the ground are interspersed with scenes of there being no snow on the ground.
When Hannah has the coach's phone, the text from Boomer56 says 'defence' the first time and 'defense' at second glance.
Carl is shown making a successful layup during the basketball game. The next shot of him immediately following the throw has his arms position inconsistent with him having just thrown a layup.
At 22:30 there is a view of a shop called "Cookie Jar" in what appears to be a high rise building. There is also a high rise building in the background. This view is clearly a metropolitan city, not rural Eden Lake.
When the murderer is trying to get out of the high school, he takes a gun past a door equipped with metal detectors without setting off any alarms.
Mason's son is referred to as Carl Kimball throughout the movie. In the end credits and on the printed basketball team roster, he is listed as Craig, not Carl.
When Mr. Rutledge is introduced on the newscast, he is referred to as Charles Rutledge. When Mason tells Hannah after the basketball game that Mr. Rutledge is ill with food poisoning, he refers to him as George Rutledge.