Jobs where the expectations of the position aren't clear. The person hiring you should be able to give a clear idea of your responsibilities are day to day in a practical way. It shows that the company understands what it wants out of the position.
I've worked a couple positions that had a really hard time figuring out who was supposed to do what that lead to a lot of confusion and both of them had this in the interviews. If the company you're working for can't define what success in that position looks like you won't be able to either.
usually its hr that doesn't know and is putting out the job description. sometimes that just shows that hr and management don't really talk a lot, or hr isn't always on site. could be red flag, could not be...