java.lang.IllegalArgumentException: Comparison method violates its general contract, only in particular test case

Here is my comparator function:

Arrays.sort(intervals, (a, b)->{
    return (a[0] > b[0]) ? 1 : ((a[0] < b[0]) ? -1 : ((a[1] > b[1]) ? 1 : -1)); 
});

I think I've clearly specified return value for each condition in a case when a and b are arrays of size 2, but I don't know why I'm getting this error in a single test case while others run properly:

java.lang.IllegalArgumentException: Comparison method violates its general contract:
    at line 903, java.base/java.utili.TimSort.mergeHi
    at line 520, java.base/java.utili.TimSort.mergeAt
    at line 448, java.base/java.utili.TimSort.mergeCollapse
    at line 245, java.base/java.utili.TimSort.sort
    at line 1442, java.base/java.utili.Arrays.sort
    at line 3, Solution.merge
    at line 54, __DriverSolution__.__helper__
    at line 84, __Driver__.main

If you had failed to cover a case, your code wouldn't even compile.

As is, your code compiles, but it doesn't fulfill the requirements of a compare method. Different problem.

Here is the general contract:

1. If a<b and b<c, then a<c.
2. If a==b, then compare(a, b) must return 0.
3. If a<b then b &gt; a.
4. you may throw exceptions if you want.

You've broken the contract: If I pass the same value to your compare method, the final case occurs, and -1 is returned, which is saying: 'a is below a', and that breaks the rule.

Expand that last node (the -1) to: (a[1] < b[1]) ? -1 : 0.

There is no symmetry when a[1] and b[1] are switched. The following would solve that.

return a[0] > b[0]) ? 1
       : a[0] < b[0] ? -1
       : a[1] > b[1] ? 1
       : a[1] < b[1] ? -1
       : 0; 

The Comparator class should be used for such structural comparisons.
Something like:

Arrays.sort(intervals, Comparator.comparing(c -> c[0]).thenComparing(c -> c[1]));