Thanks for the hint. Lot to read now, no boring weekend 
I’m interested in the modem.zip as it might solve the issue with random reboots.
I’ve switched from FOS to LOS mid of January.
The latest modem.zip on
https://io.pinterjann.is/public/misc/fairphone/modem/
is from November 7th.
This version should already be available on my FP2, received via standard FPOS OTA updates.
As it is asked in
How to know if a new modem.zip version is available?
Can this be found somewhere?