I moved this to #software:bug-reports and put it in the #bugslist::tag as this seems to be a reproducible issue with FP Open OS. (It has been reported in self-compiled versions and in the beta tests before.)
I believe everybody running FP Open OS is affected, but if you have set date & time automatically, have a SIM inserted and a good connection you won’t even notice the issue. However if I remove my SIM or am in an area without reception my FP2 resets to January 1st 1970 every time and that means that many apps won’t work until you manually set it back. E.g. Firefox tells me it won’t load forum.fairphone.com as the security certificate is only valid in the future. (don’t remember the exact words).