This is in the AP Computer Science Principles course, but is probably also the same in AP Computer Science and the Intro course.
The Exercise directions for this say:
You’ll need to write multiple functions in order to solve this problem.
They do not say that the autograder is expecting 5 functions. This all but encourages students to create designs that use 2, 3, or 4 functions and then to find out, after their idea works, that it is wrong. Five is such an arbitrary number anyway -- why not 4, if it is well written and well thought out? It's an interesting discussion to have, but not when the answer is "Because CodeHS says so."
Based on last year's interactions with students, it would be a lot friendlier and save a lot of time and frustration if the exercise directions matched with the expectations. For example:
You’ll need to write multiple functions (at least five) in order to solve this problem.