Hi,
There have been a number of similar reports recently and I have seen some cases myself. From the symptoms it may be a problem similar to these:
in which case you’ll need to
take steps to identify that the problem is with the main board : for help with this if possible, look for a Fairphone Angel in your area (see fairphoneangel )
if so, you might consider attempting a reflowing as described here
or enlist the help of a qualified repair shop (including Fairphone themselves but not under guarantee), but make sure you agree to the terms beforehand.