This is very delightful. As minimalist as possible.

The Kata has been solved more than 22k times, but it starts to fail only on your attempts :D

Your code doesn't return the right answer, tests are fine and this is not a kata issue. If you get another result with the same code elsewhere, it's probably because a different version of the language is used. sort (not stable in Node 10) may be the cause.

I am 100% certain, the kata has errors:

Here is proof:

Examples 1:

It should work for random inputs too: expected 823 to equal 328.

823's next biggest is 832.
And if the kata means 328, then 382 is the next biggest.
Both ways wrong.

Example 2:

It should work for random inputs too: expected 87050867 to equal 87050768

87050867's next biggest is 87050876.
And if the kata means 87050768, then 87050786 as the next biggest.
Both are wrong.

Your solution takes ages for n=1234567890.

Your code being too slow is not a kata issue.

Same!