I had the ST16 on the front seat, I wanted to give it as much of a view of the sky as I could because the metal car roof blocks GPS -- too bad the ST16 doesn't have an input for an auxiliary GPS antenna, I have a couple that I could have used. I also wanted to be able to glasses nce at the screen and make sure the THP was actually following me.
Anyway, I am not sure exactly what happened. The ST16 could have lost GPS lock, the control link between the ST16 and THP might have been blocked, or it could have been a combination of those things. When I realized that the video feed stopped, I feared the THP had hit a tree, so I stopped the car, revered a short distance to a place where I could pull off the road, and then tried to locate the bird. Luckily I found it hovering, but at some point the failsafe mode would have kicked in and it would have tried to fly to the last known location of the ST16 on a narrow road with tall trees on either side, and I was flying with Obstacle Avoidance off because that limits the flight speed too much.
Anyway, I re-established the connection and put the THP in Angle mode to fly it back. I had a brain fart and didn't use the video feed for that, and it took me a couple of seconds to get my bearings -- I initially flew further away before realizing my mistake. Fortunately I watched a video some time ago that taught a technique for flying a drone home when you can't tell its orientation.
I'll upload a video of my test to Youtube and will edit this post to include a link.