Interesting issue Frank, I am having what appears to be a similar issue. The first time it happened I was flying and it was still recording So while in flight I closed and reopened the SOLO APP. And then, right there I had video again, all appeared good and I was happy. However about 30-50s later the Video would drop out again (go black) and I would repeat the last task again- close and restart APP- Then all good again for a few seconds.. I would then try this on the ground - connect everything- everything WiFi connected - Good live video streaming, all good and then it drops. Controller, again, says what it always says- connection lost-WiFi off. Well I used another app to check the WiFi (that which is transmitted from the Solo controller SOLOLink_xxxx) and the controller is transmitting WiFi perfectly. I tried a few other things without success- Worked with 3DR chat services more than 3hours- they were very courteous and patient with me and my issues, yet to no fix.
Later that night I got to thinking... I tried using another Phone and loaded the SOLO APP onto it and restarted the process and much to my enjoyment, all remained connected and all has been good ever since.
The first Cell phone I was using was a Samsung S4 and the second one was also an S4... and both are pretty much Identical. To this day I cannot figure out why one drops my Video/WiFi and the other does not.. I'd really like it all to work with the original Phone. Or I just might by in the shopping mood and get a nice tablet anyway. (Any one have any great tablet choices they like) .. the only requirement is that it must verify-ably work with the 3DR SOLO APP.
So in summary Frank- (sorry to run on and on),,,
Try using a different device running the SOLO APP and let us know how that works for you.. I am most curious..