- How did they find Lockjaw, and why did they feel the need to bring him to Arnold's party?
- Maybe Lockjaw continued to visit Hillwood after Arnold released him from the aquarium?
- How did the Green-Eye people manage to keep all those people alive while they were in comas?
- If I recall correctly, the Green-Eye people apparently live in some area where time passes slowly, at least according to one Hey Arnold episode
- The original series takes place in the 90's. The movie supposedly takes place a year later but Rhonda has a smartphone?
- This was likely done to make it feel less dated and to try and appeal to a younger crowd in addition to older fans. Technology Marches On and all that.
- What grade does P.S. 118 go up to? Most elementary schools go up to 5th or 6th grade. There was never any mention of 7th graders there before. Patty was seen happily running into the building at the end (Arnold and friends were starting 6th grade at that time,) so did she get held back again? Or does the school go above 6th grade? Wolfgang, Edmund, Ruth, and the other 5th and 6th graders weren't shown going into the school at the end, just Patty who was in 6th grade during the rest of the series.
- Maybe Patty failed a grade?
- How in the world, besides "because plot", does anyone buy the whole "Arnold was in league with me this whole time and fully intended to lead you to your doom!" thing? Especially best friend Gerald and Helga. Arnold has proven repeatedly that he is almost unhealthily dedicated to helping others so "oh; this guy must have tricked him!" is an obvious leap.
- How did Lasombra know where Arnold lived, let alone what school he went to?
Headscratchers / Hey Arnold! The Jungle Movie