Previously I was creating ad units in pubCenter and it worked fine. But this time I decided to do it in DevCenter. My app is already published. It has an adControl with proper app ID and ad unit ID. However no ad is showing up. But it's ok, I'll wait some time, maybe my app should get more downloads.
The problem is: how can I track statistics for ad created in DevCenter? I can't find it there. Only the info in details that my app has some add unit. There is also something like "Ad mediation", but I'm not using it. I just use Microsoft's ad. When I log in to my pubCenter account, I can see my app listed, but without ad units.
So, the answer for today is: do not create ad units in DevCenter. Because they don't work. As a workaround I have created a new app in pubCenter with a new ad unit and then used their IDs in my app. And that works.