I just watched your video... To start with...I believe this is something dji will cover based on what I saw in the video. Now my thoughts on what may have took place. I'm guessing you are using android setup. It seems currently 98% of all Mavic issues are related to the android 4.0.2 app. Next I'd say after you upgraded the firmware and app software that you failed to go through calibrations. It's always extremely wise to calibrate the (R/C) Remote Controller, Compass, and Gimbal. The IMU and Sensors are generally the least important in a upgrade setting. Had there been some type of crash involved, then of course calibrate everything. In your case, it seems the communication between the (A/C) Air Craft and R/C became corrupt for some unknown reason. The fact that the A/C was NOT responding properly to the R/C commands, is what leads me to come up with the above details.
There is one of the main flight logs on the device used to host the dji GO4 app. The one I'm referring to is a TXT file and located in the DJI/djiGO4/FlightRecords directory. The file will appear similar to this: DJIFlightRecord_2017-02-20_[18-20-45].txt
If you save that file, let me know and we'll look into things further.
-Frank
Btw, if you did not calibrate the compass from the new location you were at, then it's very possible the A/C was heading to the last location you flew at prior to the river.
