I have the same issue. USB is recognized about 1/3 of the time. I am using the USB jack that sits under the climate controls. I have tried turning the system off, plugging/unplugging, having it connected when starting the vehicle, and other things. iPhone 6, iOS 8.4.1
The only thing that seems to work most of the time (Without having to stop/restart the engine completely) is going to the Phone\Bluetooth settings, hitting Paired Audio Devices, and Disconnect. Then, with the USB cable already plugged in, about 2/3 of the times I try this, it finally detects USB as a valid source. I have managed to see both USB and Bluetooth both available as a Source about once, ever. The connection seems to be charging at all times, despite what the Audio Source is doing, so I know part of the cable is working. I will be trying another cable, just in case, as USB cables can certainly be very funky too.
Yesterday, the music I was playing from the iPhone, USB Source, kept pausing when Google Maps would attempt to voice navigation direction, but no sound would play. The music would then remain paused. That same trip, after being stopped at the dealership for a while, everything worked fine after restarting the Renegade. Nav directions were spoken with the music merely lowering in volume for the direction, then returning to the correct volume. No pause or any other odd behavior.
Needless to say, the intermittent nature of the connection is making me nuts. Granted, the only thing that seems any different is not being able to see the Album Artwork in the display when the Audio Source is Bluetooth, but it still makes me nuts.