As I have explained, wkppvixoyxzzzzzzzzzzzz is not valid because between ixoyx and zzzzzzzzzzzz there's 3452 which your code should read because the kata asks you for the longest k consecutive strings. Consecutive is when they are following one another in uninterrupted sequence/order.

Your solution skipped 3452, going directly for zzzzzzzzzzzz. You shouldn't be able to do that considering it should be consecutive strings.

From the array, the possibilities are:

["it", "wkppv", "ixoyx", "3452", "zzzzzzzzzzzz"]
 ___________1__________
       _____________2__________
                _______________3_______________

1. "it", "wkppv", "ixoyx" (length 12)
2. "wkppv", "ixoyx", "3452" (length 14)
3. "ixoyx", "3452", "zzzzzzzzzzzz" (length 21)

Therefore, the answer is "ixoyx3452zzzzzzzzzzzz".

Not a kata issue.