Episode #1.7 - S1-E7
Other mistake: Surveillance cameras are shown on monitors when the mass panic kicks in even though any chip-dependent electronics shouldn't work in the game world (previously stated by Chotu). (00:08:20)
Episode #1.1 - S1-E1
Other mistake: Weol-ju goes into the forest at night and sees her house has been set on fire. From where she is standing, there is a large distance between her and the house, and the fire is so huge, that she can see it all the way from the forest. She then runs back, and given the distance between the forest and the house, should have taken a while, but the house is still in the middle of burning down when she arrives. The fire should've definitely worsened during her run back to the house. (00:12:23)
Other mistake: Jesus leaves his home with a double barrel break-action shotgun and an ammunition belt holding extra shot-shells. In the next scene Jesus is walking in the street with the shotgun and no ammunition belt, it magically vanished. The shotgun only has a capacity for 2 shot-shells, then it needs to be reloaded, or it can be reloaded after one is only fired, that procedure is called a top-off. He fires 1 round at the mayor and two inside Elena's home which makes three. He never reloads. (00:32:50 - 00:34:40)