Thank your for the reply.
Background setting is enabled when highlighted in blue. Here is what Apple says about the mode:
Enabling this mode does not prevent the system from suspending the app, but it does tell the system that it should wake up the app whenever there is new location data to deliver. Thus, this key effectively lets the app run in the background to process location updates whenever they occur.
However, I think that you should use the Background plugins (especially the one that keeps whole app alive) I posted and experiment with them since you have troubles sending data in background only.