I'm using Excel 365 (aka Excel 2016 I gather).
As you see, when a ribbon is being used it is impossible to work in row 1.
This can happen if the ribbon is hiding itself automatically. When auto-hide is active and you activate a ribbon tab, it covers up the interface.
Double-click a ribbon tab name to toggle auto-hide and it should fix itself. You may need to toggle a couple of times if it's gotten stuck.
Had the following reply from the developer:
*Yes, that is "by design". The problem is, that when I arrange the icons the old fashion way (horizontal alignment), it is not possible for office to shrink the ribbon under a minimum with. (Because it's only one group).
Me too, I don't like this behavior, but no solution exist. Greetings from Zurich Marcel Derflinger*