This isn't anything other then the usual "uncommanded descent" for a Mini ... for reasons not yet firmly proven, the Mini don't manage to create enough propulsion/lift. Some thought's have pointed at the props, design wise or how they remain shape during storage/usage ... other to Vortex ring state but none of them fit fully to the symptom.
Each event like this usually shows both roll & pitch instability through out the flight ... so does your's. The Mini shall be able to reach 30 degree pitch in Sport mode acc. to spec but during your flight & the initial Sport "session" you Mini didn't manage that at all, mainly 15 degrees & only once during a short max elevator input it reached just over 25 degrees.
The critical event in your case starts at 951sec with a sudden large up pitch (Green) with only max positive elevator applied (Grey). Short after you command descent with the throttle (Blue), release it but the Mini continue to descend (Red) ... this with a heavy pitch instability. After this you only command positive throttle & elevator & can luckily gain some height & limp back to safety.
DJI have constantly answered "- try calibrate" ... if the drone still isn't lost or crashed. Once completely crashed & even lost not possible to retrieve they have so far replaced the Mini without any questions. This proves that they know more then they say about this design flaw.
Simple put ... the Mini isn't safe to fly, if you do you need to be prepared to lose it.
If you also supply the mobile device DAT log we can look at the motor rpm's & nail this event even harder ... The DAT log we need have FLY011.DAT in the end.
Check here how to retrieve it -->
Flight log retrieval and analysis guide read under point 3.
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