Billions of devices in the Mobile-App-Integration

In my Mobile-App-Integration I find 1.366 times the word “Gerät” (Device) , almost the same number of devices is deactivated by me yet. These entries come from only five real existing mobile devices. How do I get rid of them? Is there a possibility to reset the integration? How can I be sure that this doesn’t happen again?

Any hint is welcome, the solution is worth a großes Bier!

Peter