I have got this problem

I mean for example a code with only return new List<int>(){2,3,4,5,6};. You'll never get a message telling you there's more than one mismatch.

Please say which language you're using (I guess it's C#). Consider the tests will only return you the first element mismatched in case of a bad answer. Try returning always the same list and you'll see.

Depending on the language you can have some limitations, but I don't think it's the problem here. It's hard to help you without more informations! Ask a precise question (actually you don't even ask one!), say which language, which cases, etc. And maybe you may post your code (with a spoiler flag) if you cannot get out of it. Also,see if this may help: https://docs.codewars.com/training/troubleshooting.