This has happened a couple of times, so it's not a one-off. The App Store icon has a badge showing there are new updates available. Click the icon, the app opens but the Updates page is empty "All Apps Are Up To Date". Tapping the Updates button, or switching to another page, e.g. Charts, and back doesn't change this. The only way I can get the updates to appear is to kill the app (double-cick the Home button) and re-start it.