UPDATE:
After contacting 3DR, and on the phone for an hour with 3DR support, which by the way was very professional and helpful, the problem was determined to be caused probably by a Controller/link failure. I meant to make mention, the battery was at 60% after the climb, then the Controller display back-light turned orange and the displayed data froze. Also, on the tablet the telemetry data fields went to what I can describe as garbled although still receiving telemetry from Solo. I immediately hit Home and Solo did not respond right away, so I held down the Fly button to Land Now. We are not sure just what happened, but Solo finally responded and came to the vertical home point, probably by initiating an auto RTH, and by that time the battery level had just dropped, I had no control - even tried Manual to no avail.
Then, after powering off Controller and hooking it up to the charger all I got was blank/white display - not even a battery charge indicator. Pulled Controller battery and re-installed, same thing. After I got home I pulled the Controller battery overnight and re-connected battery, now it's LCD flickered some data then came 'up'. Controller still does not accept a full charge as shown on the 'charger connected' icon, nor will the Controller COMMUNICATE with Solo even after a full reset. So there you go. 3DR is going to inspect the Controller. I'm sure that was the issue as I've read about Controller failures elsewhere.
Should have suspected something with the Controller as I have had a temporary 'link lost' warning before with Solo just 100ft away LOS a few times in the past then the problem went away.
FYI: Since no communication can be made between Controller and Solo, even after reset, I could not even SSH into either device to attempt to retrieve the flight logs, dang it. Also during the flight I was using Alpha antenna's and had 3 bars of link signal. And yes, local ATC was notified and we flew in the exact time period we were required to, in fact the 4 days we were there, we did not observe one aircraft flying in the airspace over the private airfield.
So off it all goes to 3DR, I'm sure they will be able to figure it out. Will keep you all posted.
BTW: Did I say it was a pleasure dealing with 3DR support? I called them late at night from Florida. Within 10 minutes of the call I had an email containing exact shipment instructions, a FedEx shipping label, and a Solo repair packing list indicating exactly what to ship back. Can't beat that kind of service. The email from 3DR was sent at 9:11PM, CA time. 24/7 support, where else are you going to experience that?
Cheers