I had same issues with my GoPro 3 and figured it out. Here’s what I do. Turn on controller then power up solo/drone. Open whatever app you are using solex app, SidePilot app, stock solo app. And see if video feed is working. If not then close the app or go back to home screen of app- not fly page and then carefully go over to solo drone and manually power off and back on the GoPro. After you have power cycled the GoPro reopen app go to fly screen and video feed should work.
That’s the only way I’m able to get my GP 3 video feed going and I’m assuring you it will be the same for you.
Only GP4 black, ect,, work without doing this power cycle thing.
Good luck