Not an issue

me too！

This is a CodeWars framework glitch, not a problem that should be an "Issue" with this Kata. It happens when the AJAX session to the server is lost (logged out, inactivity, I dunno).

It happens occasionally and the first thing you should always do is select your whole solution and copy it onto your clipboard. Normally your unfinished work gets saved over the AJAX connection (and appears in your "Unfinished" list in your user profile) but once the AJAX connection is lost it won't continue to capture any further changes you've made.

Refreshing the page gives you a fresh AJAX session and almost always fixes this (you might have to log back in, but not usually in my experience). Once the page reloads, delete all of the old code left in the solution box and paste in what you copied from your clipboard. Then try submitting it again.

I had such problem. Sometimes site logs you out (or your cookie expires, or whatever), but you can't notice it while you work on a kata, except the fact that you will be getting "Unknown error" all the time (and tests will run OK). But if you refresh page, you will be prompted to login (and all wil go back to normal).
If this won't help (I had this situation once, on another kata), try clearing cache and offline website data and refreshing page.
Copy your solution to clipboard before clearing and refreshing. Just in case.