Whether it occurs or not can depend on the specific data being processed, and the order in which it is being processed. So this can happen in production after seemingly working fine for a long time.
I haven't personally encountered a buggy comparator without a total order.
To give one example, a common error is to compare two int values via subtraction, which can give incorrect results due to overflow and modulo semantics, instead of using Integer::compare (or some equivalent of its implementation).
Another common source of comparator bugs is when people compare floats or doubles and they don’t account for NaN, which is unequal to everything, including itself!
In Java, the usual symptom of comparator bugs is that sort throws the infamous “Comparison method violates its general contract!” exception.
I recently wrote a blog post which (while not the main focus) includes a discussion on randomized testing of sort algorithms in the face of inconsistent comparators: https://sunshowers.io/posts/monads-through-pbt/ section 2.