I'm pretty sure adware is being loaded via the Samsung Galaxy Store. I've read through two pages of posts (and had the same issue). I dumped a bunch of recent aps and then remembered that I downloaded a kind of pointless drawing app from the Samsung Store. That's when the ads started. So I...
I see the same problem. If I delete a few items from the Spam list (under settings), I can mark more spam.
I think there is a memory limit on how big a spam list the software will accept. I'm looking for a way to make the limit higher.