Since you fail the random tests I strongly suppose that you modify the given input (for example you reverse it in place) and so the reference solution for the random tests doesn't work on the "good" array. Work on a copy of the given input. Cheers.

@BruiserMcCruiser: I slightly modified the tests (Should -BeExactly instead of Should -Be) hence some solutions are invalidated.
Thanks for your post.

Did you try turning it off and on again?