I just posted about Midi not working when the USB cable is plugged in. I thought this was but and need to be fixed. Come to find out, as I read through the manual thoroughly, this is a normal operation. See the attached image from page 27 of the manual….it was still frustrating to go through though. Why wouldn't the DIN MIDI input work while USB is connected? Not sure, but it is what it is.
Sorry about your frustration. The USB MIDI precedes the 5-PIN MIDI. You can only use one of them for MIDI communications.