In the first episode, Gi-hun types his PIN code, 0426, and says it's his birthday, i.e. 26/04. But here, at the 3:50 mark, as seen on his computer file, his birthday is on 10/31. This is confirmed in episode 5 in his file in the binders.
When the policeman is hiding behind vans on the ferry, two of the vans have the same number plates.
During the candy-breaking scene, the initial shot of the playground area shows an umbrella on the wall with no grooves at the bottom. The next shot has the umbrella with grooves.
Prior to commencement of the 2nd game, Sang-woo is recalling his childhood memories of running with his friends to a man who is melting sugar. Immediately after this scene, the four symbols on the walls of the game room are shown, however the umbrella symbol is of a different design to that seen in all other shots.
The amount of honeycomb removed changes when Gi-hun is being watched by the guard.
With workers above and on the same level as the vans, it is completely implausible that none saw the violently shaking van, during the scuffle with the detective.