Daniel tells Kumiko he is the same age Miyagi was when they met. Pat Morita's actual age was the same as Ralph Macchio's current age when Karate Kid was filmed but Miyagi was supposed to be older since he fought in World War II and Pat Morita was actually only between ten and fourteen years old at the time. Also Daniel is supposed to be seven years younger than Ralph Macchio's actual age.
During the interaction between Robby and Kreese in the prison, a woman can be seen talking to an inmate in the background. In the next shot she was sitting alone at a table, then after the camera focused on Kreese again, the inmate was back in the same spot.
Miguel's physical therapist drives a Nissan Leaf, an electric car, but when he starts the car to drive away, it clearly makes the starting sound of an internal combustion engine.
When Miguel is reaching for the magazine and his wheelchair falls over and he is lying on his side on the ground, his left leg bends upward toward his torso in a motion impossible during paralysis.
At 24:06 when SJDC inmate Shawn pushes Robby out the door and into the wall across the hall next to a cell door, you can see the door pop open. In the very next cut, the door is closed again. Being it's a metal LOCKED cell door, it's unlikely it would pop open.
When Johnny visits Ali Mills' Facebook profile, her statuses and photos/posts all have a locket icon next to them. That locket icon is the sharing setting for "Only Me", meaning that Johnny shouldn't be able to see the content - only the owner of the profile can see these.