This is most presumably coming from your code. To raise an issue, you must prove there is an issue, see there: https://docs.codewars.com/training/troubleshooting/

If the problem required a more efficient solution then I would agree with Danil, but getting a brute force solution to this is not terribly difficult.

This is really basic maths stuff, the kata does not require real optimization, many 7 kyus are harder :)

No, 6 kyu is ok.

the two arrays have the "same" elements, with the same multiplicities

two 2 and one 3 -> one 4 and two 9

Not the same multiplicities.

Not an issue, maybe you should read the description again.