What does it say on the splash screen of the Android app?
Screenshots attached for JRemote2 Ver. 2.3.1 Android app on phone:
1) Row of audio app icons on phone's home screen
2) Opening window
I do not have JRiver For Android installed.
In my experience, at any given time either the first three music apps all work (i.e. connect to PC MC server and play music, usual case) or else all do not work.
If you suspect a problem with JRemote2, then give one of the other apps a try. If it also has a problem, then that most likely indicates an issue in your system, either with the phone connection, the server, or your renderer. If the other app works, consider re-installing JRemote2.