This is normal. The VPS is only good from around 30 feet and below. Often, the logs will show VPS working as you climb close to 100 feet. From that point the logs will always show VPS=0 until you get down to around 30 feet. At which point, it is more accurate then the barometric altitude.
In this case, the barometric altitude is irrelevant. In mountainous areas, people may take off and land at different elevations and landing still works properly. The VPS altitude is used for landing (on those drones with VPS sensors).
It landed because of two things:
- The conditions were just right to cause the VPS sensors to show 0 (zero) feet altitude.
- The left stick was held down long enough (while VPS=0) to trigger landing mode.
It went into landing mode prior to losing the signal.
For your own benefit, you might find it interesting (now that you know how to access your log files) to analyze some of your older log files of the same area. Then, check what the VPS altitude was while flying at the same location as this indecent. My guess is that in your other flights, the VPS was not showing zero at that location.
I’m glad you found your drone. It may be salvageable (except for the battery).
I am not an expert at deciphering log files. There are some people in the MavicPilots.com forum that are. If you want more details than what you are getting here, you can post the PhantomHelp link there with a short description in the “Crash and Fly Away Assistance” section.