This is very interesting.
I have had this experience, more than once. I was using Go, not Litchi. What is in common, is the drone suddenly ignoring the remote, gaining altitude and flying off to wherever the mood took it. I am trying very hard to find out why. In each case I was able to recover the Phantom, barely, but as much by luck as anything. In no case did GTH work. Changing to ATTI mode gave me some sort of intermittent control, even though I was line of sight, (stretching it when the drone had flown as high and far away as it chose to) but, by the smallest of margins, landed it somewhere recoverable. A perfectly normal flight, everything going smoothly, and then this sudden mad flight. At first, no responsiveness to the remote, and then, sometimes responding, which enabled me to point it the right way, suggest it go "forwards" and "down". After that it was all luck.
I have toyed with many theories as to the cause. I don't know. I'm pleased to find I am not alone. It is very disconcerting as I don't know when it will happen. The worry isn't just losing the drone, but if the battery dies before my little random bits of control point it somewhere safe, the damage done could be anything. It doesn't happen often, it happens rarely. But more than once to me. But I don't want it to crash into a, well, anywhere bad.
site guy, did you ever get to the bottom of this? Did your logs get analysed by someone, and did that lead to a solution, or even an explanation?
Would be good to share with all. You said you still had plenty of battery, I can tell you it is much scarier when the battery is low.
I can just imagine standing in front of the FAA and the Judge and saying "it wasn't me, the drone just had a mind of it's own", after those fast spinning blades come crashing down in a playground.....
Really keen to learn how to not have this experience again.