You probably debugged your solution somehow incorrectly. Tests do not fail for [1,2,3,4,5,6], but for [8, 0]. Expected answer is 0 (sum of elements to the right of 8 and to the left of 8) is equal, but your solution returns -1.

Not a kata issue, your solution is incorrect.

C# version of the kata works good for me. You are either misinterpreting the logs, have some bug in your solution, or kata has some bug which does not manifest for every solution.

If you are 100% sure your solution is correct, post it here (see here how), and someone will check what's wrong.