In high mountain (2300m) I noticed a rather stressful phenomenon: my MM started a descent of 60 meters without any action on my part.
Noticing this after a while, I activated the ascent with the RC.
My guess: I was sheltered from a fairly strong wind which created a depression that the drone wanted to counter with a descent. What do you think of that interpretation ?

How did you measure 60 meters?

You should post the flight log.  If the fall was really that long it's not the usual air-speed delta design flaw (which is pretty limited).

What do you think of that interpretation ?
Like most drone incident guesses made without seeing the evidence of the recorded flight data, it's not correct

Indeed, a data log would help. it should be noted tho that the max altitude of the MM according to the specs is 3000m above sea level, so while you were flying within specs, it‘s at least reasonable to believe that the drone is more prone to be affected by adverse wind conditions at 2300m,right? But again, the log will show whether the drone decided to descent for some reason, or whether it tried to keep the given altitude but was unable to do so. Or maybe the drone wasn‘t aware it was descending...all that could be true.

Post the log here - http://www.phantomhelp.com/LogViewer/

Hi. Thank you for reaching out to DJI Forum. With regards to this concern. May I know did you encountered any notification or prompt when this happened? Please try flying the drone in a different location to isolate the issue. Please keep us posted for further assistance. Thank you.

My data :
https://www.phantomhelp.com/LogViewer/ZP2NVJA9U1WDU8V0FYJR
line 3780-5000

Incautious usage: it's a little ultra-light pocketable drone.

Flying above 2000mt with limited battery (cells depleted at about 3.4 Volts when first happened), predicted wind gusts of 9 m/s, recorded THOUSANDS of warnings, which were disregarded, auto-landing for battery depletion in the end.

You definitely didn't "volez avec precautions". Draw your consequences. You're lucky to still have the drone with you.

yes, i'm guilty ... thanks for scolding me.
my post had 2 objectives: find the explanation of the phenomenon and warn of the possibility of encountering this event.

You asked for an interpretation. No scolding here just analysis.

I imagine you were after some comforting explanations but I am afraid it wasn't the Mini's fault. If you're ready to learn from it, no excuses, you can become a better drone pilot. Good opportunity to start following all the good safety and common sense practices, not least reading the manual.

I'm very reckless with my drones too. But I do accept the blame when (not if) things go wrong ;-)