There are some important points that would help to avoid incidents like this in future.I had been watching a lot of videos about controlling the drone and doing a lot of trial runs to avoid this so feel extremely incompetent at this point in time. I sort of hope it isnt wind again but am guessing that is what happened.
The Mini is a low-speed drone and is poorly equipped to come home against significant winds.
The wind up high is always going to be stronger than what you are feeling down on the ground.
When your Mini loses signal and is trying to come home in RTH, its top speed (in still air) is only 8 metres/sec (18 mph).
Pushing against a 4 m/s wind (9mph) will halve the RTH speed.
In your flight, the Mini was 138 metres up and only making 1.5-2 m/s coming home, between gusts.
During gusts the Mini was being blown backwards at 2-2.5 m/s.
If you fly off downwind into the distance and have trouble coming home, the battle is already lost.
You have to prevent getting into that losing situation and avoid flying off downwind, particularly flying at higher altitudes.
Flying lower will usually put the drone where the wind is not as strong.
Fly into the wind going out.
It might be slow, but the return will be easy.
Doing it the opposite way is asking for trouble.