This is a known issue with the recent release of App World. When you open up App World, hold left “Alt” and type R S T. This resets app world. After you do this, go to My World and after is refreshes, it will show you all available updates.
I do this almost every other time I open up App World. Yes it is a pain and not the way we should have to do it, but this is the only way until it is updated/fixed.