I have a solid number on my Coverage Unit and bars on my Window Unit, but nothing on my mobile device!
First, make sure that your phone is NOT on LTE. The RS2 systems does not support the LTE technology.
Second. Once a mobile device has repeatedly found a signal it can tend to remember this signal and not look for a new signal. Restarting the phone can often force the phone to look for a new signal.
Go to the location of your Coverage Unit and simply power off and back on your phone. You might have to do this 2-3 times for the phone to recognize the new signal.