Ionic app works fine on browser but does not open on my phone

My project works fine with ionic serve , but when I generate .apk file with ionic build android and install on my phone or run in emulator the app does not open and stay on a totally white view.
Anybody can help me?

I’m beginner here.

I have more or less the same problem! I´ve got a geolocation app, which works fine in ionic view,
but when i install the apk on my android it only shows the headbar, not the map…
Any tips & input would be very much appreciated!
Tx hanna