Your code does not conform to all specs and does not handle some cases correctly. In this paragraph you have some hints how to debug your solution. You can also read the description carefully again and make sure your solution handles all requirements.

It is a problem with the solution, not a kata issue (although I agree that the input is terrible).

It's difficult to help you without your code. (Please see documentation how to use code formatting)

I don't do C# but it seems that you are adding unicode characters between the alphabet positions in your solution.

Please do not raise issues without mentioning your language and showing your code. It's useless.