I also have sporadic advertisements on my start bar (when I press the win key), sometimes it suggests an app, which looks just like any other app, the only difference is a "SUGGESTED" header which is easy to miss. I assume when you click on that, it opens the store app.
It appears at the very top and AFAIK there's no way to disable it.
It appears at the very top and AFAIK there's no way to disable it.