Ok, if nobody has a specific idea, then I think your options are …
Getting assistance:
- contact fairphoneangels in your vicinity, if there are any (they are community voluntaries offering support in their spare time). They could perhaps help to identify a particular module causing the problem by swapping, or they could perhaps assist with other options.
- contactsupport (official Fairphone support)
Generic do it yourself stuff:
Make sure you have a backup of all your important data, then
- Disassemble the modules of the phone, you are allowed to do that without losing warranty. Clean the contacts connecting the modules with cleaning alcohol, then reassemble the phone. Here’s a nice video …
- If that doesn’t help, try a manual re-install of the OS (“The user data will not be erased.”)…
- If that doesn’t help, try a factory reset ("which will remove all your personal data.") …
- If all else fails, here’s how to really start from scratch …
If the last three options (all software) don’t help, it’s most probably a hardware problem, and you would be back to getting assistance.