Setting up for a gig tonight, I could not get my IPad Pro to recognize my usb c dongle, head phone out or charge. I tried 2 dongles and audio cables to no avail. I have my iPhone set up for a backup, as soon as I plugged it in. It worked right away. I did upgrade my iOS on my iPad a couple of days prior. Everything seemed to work fine. Maybe I have a dirty port? will check tomorrow. Any suggestion welcome.
iPad not recognizing usb c dongle.
Might indeed be a problem with the usb-c socket in your iPad. In the worst case you will need to get it fixed at an Apple Store.
Thanks Peter, undoubtably the charge was working. Hooked it up this morning to check it out and realized the song volume was set to
-inf db on my sound check song. Standing on stage with 5 mins til start time and everyone staring at you, you can overlook the most simple solutions.
I have been using ST3 for about 8 months now and absolutely love it. You have made my life so much easier. Keep up the great work. You are greatly appreciated.
Ronnie hey Ronnie I know that feeling, last gig same thing with both my remotes that would not work 
on stage ready to start but no way could I work out the problem , thanks to the iPad interface it saved the day , then at home it took me a short time to realise the issue was all my programming of foot pedals were cleared due to an upgrade and I didn’t think of testing the pedals before a gig, but ST3 came through again it still got me through the night and not many people noticed the difference, thanks to its bullet proof design and I still had my iPhone as an absolute god help me backup so I did not panic too much.
Love it 
a year later
I had a similar problem. I went to iPad settings for sound> headphone safety> headphone accessories and selected "forget all usb devices". Started working again after that.