macOS Sierra Spotlight search does not find Numbers but Number My Spotlight search behaves strange and I don't know how to fix it. 
Any Ideas?

When I want to open Numbers, I hit command space  and start typing "number",



but if I keep on typing the "s", essentially completing the app name Numbers, Spotlight does not know what to do anymore.



Does the index point into a wrong direction? If I search for a specific file it works.

I tried the solutions by Anil and Senseful here, but the problem does not change

UPDATE

After rebuilding the Spotlight library the problem shortly disappeared (one week). But it returned again. So maybe my question is not how to solve this problem but what is corrupting my Spotlight index?

Interestingly the Spotlight results look a bit different now and shows the App-Store Numbers version (which then automatically opens the local one).
I would start by rebuilding the Spotlight index.

From: How to rebuild the Spotlight index on your Mac


  
  Choose Apple menu () > System Preferences, then click Spotlight.
  Click the Privacy tab.
  Drag the folder or disk that you want to index again to the list of locations that Spotlight is prevented from searching. Or click the
  Add (+) button and select the folder or disk to add.
  To add an item to the Privacy tab, you must have ownership permissions for that item. To learn about permissions, choose Help
  from the Finder menu bar, then search for “permissions.”
  From the same list of locations, select the folder or disk that you just added. Then click the Remove (–) button to remove it from the
  list.
  Quit System Preferences. Spotlight will reindex the contents of the folder or disk.
  


Or via Terminal:

sudo mdutil -i off /
sudo mdutil -i on /
sudo mdutil -E


See the man page for mdutil or type man mdutil in Terminal.