I have a Native App that runs fine on iOS and on most Android. On some Android devices I see:
The the connection to the server was unsuccessful. (https://localhost/index.html)
when the app is starting.
This is happening at runtime, right?
If so, it probably has nothing to do with VoltBuilder itself. Next step will be to see how you can reproduce it, so you can narrow in on the cause.
Google is always good for checking on errors just prefix your search with something like Cordova. I searched and found this amongst many other threads cordova android application error the connection to the server was unsuccessful - Stack Overflow