I received a small project task with very specific instructions about what they want to see in a solution. The task used a synthetic dataset with very obvious patterns and did not take too much time to solve, although writing a thorough description of my analysis did. Several days after my submission I received an answer that "our engineers did not find that it met the criteria that we have established for submitted solutions". I wrote back requesting more feedback, but was ignored. In the end I feel that my time was wasted completely, because the task appeared to be trivial and hence uninteresting, there was no reason to research any advanced techniques to solve it, nor did it call for any clever engineering solutions. It's hard to tell what exactly they were looking for in a potential candidate.