When Mac enters the shack the snow on the floor clearly shows an outline of furniture which must have been present when the snow effect was applied but removed before filming. The outline is not present in later scenes.
After Mack comes back to the lake from seeing Wisdom, he and Jesus decide to race each other on top of the lake. At first you can see Mack to the right of Jesus; and, when the angle shots change, he's on his left side; and, when the angle shot changes back again, Mack is again to the right of Jesus.
When Mack walks to his neighbor to ask him about the note, the driveway has two paths through the snow on the driveway cleared; when he returns, the entire right side of the driveway is clear.
When Mack is at the shack and has a breakdown, he throws a few pieces of furniture against the walls and lays down on the floor. At that point he is the only thing on the floor, however when he wakes up at the end of the movie, there is a standing chair next to him.
When Mack leaves the shack, he wears a beanie (woolen cap). When he arrives at the vehicle, he isn't wearing it, and there is no apparent reason he would have taken it off since it's still snowy.
Several of the sheriffs/deputies have a US flag on their right shoulder which is flying left to right. On that shoulder, the flag should be 'reversed', right to left.
In the entire movie, God is portrayed from a Christian point of view (Jesus, etc...). The prayers at Missy's funeral toward the end that can be heard in the background are the ones recited at Jewish funerals and have no connection to Christianity whatsoever.
At 1:08:31, Sarayu is gardening with a hat on, but at 1:09:51 she takes her hat off.
When Josh and Kate left Multnomah Falls to race to the car, they headed off to the left. That is the path heading up the mountain, you have to go to the right to get to the parking lot.
It's hard to imagine that FBI agents would invite a grieving parent to the scene where his abducted daughter was assaulted or killed, leaving behind her blood and dress.
Sam Worthington's Australian accent shows through several times throughout the movie, despite his character, Mack, being born and raised in the Midwest.
Snow usually doesn't cover trees and plants with green leaves. The spruce trees have bright green new growth, that it is spring and not winter, as the snow would indicate.
When Mack walks out of the house after baking with Papa, the blue jay should be a Stellar's jay. Blue jays don't live in the Pacific North West. Stellar's jays live in the Rockies and PNW.