When the janitor finds Annie with Katherine and leads the Springer Spaniel away, she has three legs (at around 1h 11 mins), but in the very next scene (at around 1h 11 mins) the janitor is leading a Springer Spaniel with four legs down the corridor, which would be Max, with no explanation of what he did with Annie nor how he captured Max.
About 24 minutes into the film the boy takes off on his bike wearing blue trousers. Seconds later as he pedals down the sidewalk, his trousers are white. Seconds later after that as he enters the building to look at the dogs, his trousers are blue again. And then as he enters the room to see his dog Annie, his trousers are white again.