As well reported on the forums the FP6 had a frustrating issue that caused most (but not all) apps to not work when on certain wifi networks. It turns out, the IPv6 stack on Android is flaky, and I guess other vendors fixed or worked around it themselves.
The latest update that I got yesterday apparently fixes this for FP6 too!
Latest update for FP6 finally fixes home networking
Submitted 2 weeks ago by cm0002@toast.ooo to fairphone@hardware.watch