Yeah, someone on here once found an x-ray tetra that had been sucked under his UGF. Somehow it survived and was miraculously living under there for who knows how long. o.O We still don't know how it survived.
I also know that UGFs are famous for sucking fish in and under. There's a possibility your neons are getting caught in the filter too. That aside, I also agree with koimaiden, that there's some infighting going on.
I didn't know that those things sucked fish in! Another reason to dislike UGF. If it sucked an x-ray tetra in, it could certainly get a neon.
Billy, if you do those things, I bet you will have a much healthier tank. Can't wait to hear your results!