I suspect I found its origin. To me it looks the same as some pin that is positioned in the plastic frame:
This is what I decided to do to avoid the danger that might be my continuity tester to the Librem5. I made this little chart:
I measured the voltage between the middle pin of the switch and the other two pins. The table shows that in position 1 (up if the phone is upright) the voltage between the upper two pins is 0V and the voltage between the lower two pins 2.25V. If I move the switch to position 2 (down) the voltage between the upper two pins becomes 2.25V and the voltage between the lower two pins becomes 0V.
To me this looks like the switch is mechanically working and therefor probably not the cause of the misfunctioning of the camera kill switch.
I looked through the manual of my multimeter and the only information I found about the continuity tester is that the current used is smaller than 0.3mA - no information about the used voltage/signal. I guess I’ll have to measure it when I’ll have another multimeter around…

