Don't know if you are still looking for an answer. Mine disappeared when I added ad blockers to my browser. I removed one ad blocker all together and then disabled the other one for Hubpages.
If this is your problem, just pay attention when you disable it to see if it gives you options. Like if there's an option for "for this domain" or "for this page or website" choose domain. Choosing page or website might only disable it for the URL you are looking at, so it might disable the ads for one hub only, or for the web address that shows up when you're editing but not the final published up.
Hope this helps!