After 2 flights today (man, nice to have 3 flight batteries now), I can almost say for certain it IS a cable issue between Solo and the GoPro. How do you ask, I followed my procedure to the letter all the time, most the time it worked. NOW: I got fed up, being a test/systems engineer I paid a little more attention. You have to make sure the GoPro is located properly in the mount, and SEAT the USB connector until you feel a solid 'click' or 'snap'. Sorry, it's just by feel. I had no feed with the App running on Android until I picked up Solo and re-connected and the only way to describe it is the connect on the Solo->USB->GoPro just 'felt' more solid. It was not much, but got good instant live video feed on App/Android waiting for 'fly' or 'flight school' screen.
For what it's worth, is there a rep for 3DR lurking here? I can provide ton's of test and initial flight data, that's what I do for a living.
Also today:
Sped things up a bit in the App, now at 'medium', Solo fly's great.
Selfie mode worked
Follow me, Solo tried, but acted very strange. Back to 'fly' mode.
3DR, are you around here? - we all need feedback. I can bet my 20+ years as in test, It IS either the connection on your right angle connector to GoPro USB, or just a bad cable, internal conductor failure, or design, PERIOD. You can take that to the bank.
Cheers
---