Hi Marc and Rudi,
The app checks online at moosh.im for a new firmware version when it starts up. If there is no internet connection available to the device at that time, it will just continue normally but won’t offer update prompts. Could this be the issue? To check, make sure your device is connected to the internet (either through wifi or mobile), force quit the Mooshimeter app and restart it. If you don’t know how to force quit, you can reboot the phone instead.
I hope this helps, I’m adding a note about this issue on the wiki here:
Let me know how it goes, best