It simply isn't reliable period.
Never have it follow you while you are driving with no sight on the drone. Also, having it follow you near a steep canyon wall is asking for the very trouble you experienced. I did a lot of experiments with autopilot follow me, be it with an inspire1. It followed sometimes from behind, sometimes from any side and next minute from the front. Sometimes it accelerated like mad without any reason. Luckily I was on a boat with no obstacles around. I would never have done that with trees, structures or mountains around. And I never will again. If I want to follow something I follow it myself. And following myself, well, I was never a selfie person and have no desire to start being one.
Sorry to spoil your fun but it's a gimmick at best, and most certainly not trustworthy. You are one lucky person to still have your drone! AP is wonderful for waypoints and stuff, but following is not secure, in ANY app. The GPS in your device is everything the app must rely to. And we all know that GPS in phones are not really pro stuff. Sometimes position and GPS altitude are all over the place, exactly like you show in the video. It's ok for what it's meant for, basic navigation, and more importantly, suppling a static position to ensure maximum social media advertising integration. Please don't have 100% blind faith in that the mavic will do everything it is supposed to do in every occasion. Rather, don't trust it at all and stay suspicious and alert for stupid flaws in the programming. DJI as well as Autopilot never put in the research needed to make it flawless. It would simply cost way too much. Expect a drone and software that is fully trustworthy to exceed 50.000 US$. And even then, it is always recommended to have the pilot actively monitoring the flight with the finger on the disengage button.
