I don't know, but I'm noticing the same problem! I've lost a little weight but quite a bit of fat. My abs are finally visible and I'm starting to see a six pack, except for a little fatty pouch right below my belly button. I haven't had kids so it's not because of that, but it's REALLY aggravating.
I've only lost ten pounds so wouldn't think it was "loose skin" but that's what it looks like - a jiggly, deflated little bag. Not sure what to do about it other than continue to reduce bodyfat % and continue strengthening my core.