Mac App Store shows update count but section is collapsed/empty
Had the same problem. Solved by going to the "Purchased" tab on the App Store, looking for software that needed to be updated (xCode, iMovie, GarageBand, Numbers, Pages, Keynote) and clicking there on "Update". I also started downloading a new App. Some 15 secs later they appeared on the "Updates" tab as well. Including a "Software Update" that contains a new iTunes, what I was looking for actually.