In the native mobile recources there is a widget called app events: https://docs.mendix.com/appstore/modules/native-mobile-resources
Here you have an option to do something with network events. For example call a nanoflow to change a boolean if the app goes offline, or show a pop-up message.
Hi Franz,
You could create a JavaScript action to check if you Mendix server is available too with
https://github.com/react-native-community/react-native-netinfo#usenetinfo
Cheers, Andries