I suspect your battery is not well connected. I kept getting going back to the 70s with one of my loggers for a while. It was groovy but a pain in the rump. When I re-soldered the battery connections, it all got better.
I don't know why, but now it works. Maybe it really was the battery connection. But why would it then show the right date and logg the false? For safety I resoldered the battery connections.