Unlock achievements.
Unlocked dates are made as they happen.
Dates unlocked are set to 1/1/1970 00:00.
i think this is a very well known bug. its a result of the game being unable to retrieve the achievement date from the server so it defaults to the epoch start date, which could happen from a number of things that cant really be fixed (like having a bad connection in that moment). this can happen in discord too, as well as anything that fetches stored time from a server. i would say if its continually doing this after restarting once or twice then something else could be going on here
