When Schmidt and Jenko first arriving at the school and analyze different groups of kids, an Asian girl with spiked hair wears a Panda dress. Shortly after as Schmidt and Jenko talk with Eric by the cars, a different Asian girl is now wearing the Panda dress.
When Schmidt tells Jenko that tapping Eric's phone was a bad idea, a substantial number of cops are behind Schmidt. The camera cuts to Jenko, then back to Schmidt, and fewer cops are behind him. When the camera cuts back to Jenko and back to Schmidt one more time, no cops are behind Schmidt. The number of cops behind Jenko never changes.
The text Schmidt sent to Jenko to meet him in the hallway is received by Jenko at 1:59pm. Minutes later, Eric says to them during the drug deal that he needs to finish the girl's volleyball page by lunch. Supposedly it was 1:59 but Eric reveals it wasn't even past noon at the time of their conversation.
The officers' mistake at the beginning is not accurate. A police officer is never required to read a suspect their Miranda rights. Miranda rights only become relevant when a person is in custody and being interrogated by the police. Then even if you are not read your Miranda rights, the only consequence is that the police cannot use anything you say as evidence against you.
Much of the Korean writing in the church is grammatically incorrect, the type of translation produced by online translators. For instance, the Korean version of "Aroma of Christ Church" has Christ Church as the possessive of the word aroma, e.g., "Christ Church's Aroma" or "The Aroma that Belongs to Christ Church".
When Jenko is playing with chemicals with his friends blowing stuff up he gets a bit of the chemicals on his hands. When the guys run away from the bomb, Jenko can be seen touching one of the boys arms. Covered in acid, this would clearly cause a reaction.