I got 3 more at the same time, after handing in 3 donation missions. That ain't a coincidence. (I'll post them when I get back in game later - one is a duplicate of the one I posted previously, which is currently broken as it doesn't give any message after scanning (already reported).
Ok I agree. I am getting Tip Off missions as a side effect of handing in lots of missions. I got 3 yesterday.