Today, I had a special event with Action 2.
I went for a hike and I used both the full battey (combo) and the full internal memory (offically 2 s of 4K60 left).
I imported as usual the videos, pictures and hyperlapses, and my import software said 100% was imported. I never had any problem with this soft.
Then I checked some files, and saw that all videos and hyperlapses had been imported. I formated the Action 2.
It is only then that I realized that all pictures taken after a given time were missing...

I know it is a pity that I formated Action 2 before noticing... But I  never had any problem importing files in my long life. So I wonder what  could have happened.
Any possibility that those pics could have been overwritten to make some space to finish writting a video or hyperlapse? Or a glithch due to full memory or fully depleted battery?

A wild guess - did you have loop recording turned on?

No, It was off.

It was the first time I used Hyperlapse. I took 4 or 5 short ones. One was almost at the end when the battery was crying it was going to end. During it, I had several vibrations in the device while the screen was off (I set 1 min turn off screen)... So I do not know what it was about. And I stopped it just after. There was nothing special on the screen except for the battery warning. After that I took 2 other very short video clips and there was no problem.
Does Hyperlapse take many pics, then build the video clip and then erase the pics?
Could it have erased some of the other pics if a conflict of space occurred while building the video clip? Or if the number of pics registered was different from the actual one due to battery turning off in the middle of the recording process?

I found the problem. I must have accidentally changed the settings from JPG to RAW. Then, today my soft was not importing any pics whereas they were in the cam with a DNG extension.
Sorry for the false alert.

+ Any suggestion of softs to easily convert from DNG to JPG?