Never mind. Understood

I still can't figure out when or how to decide if given string is imposible to decode. I read other answer but it still does not make sense to me. Could you provide one example(s) with calculation.

changed the comment content bcoz I could not delete it. That trick won't work for this problem but it is good anywhere else since it works for all types of arrays

You are not returning a longest possible common subsequence. Please read the description carefully. Have you read the Wikipedia article? Did you solve the non-performance version first?

This is not a kata issue; it should have been marked "question", not "issue".

I think this fact was already known at the time it was approved. Anyway, as it often happens with golfing katas, it expects a certain type of solution.
If you have something more general, feel free to submit it here https://www.codewars.com/kata/the-soul-of-wit-reverse-an-array ;-)

Have you found a solution that would work with that input and still being in the code length limit? Maybe the tests are ok for that.