I haven't experienced this with other Sony cameras (unless I took the battery out to store the camera back to the box). However, with Sony A7 Mark II, it happens a few times that asking me to reset the Date and Time after I switch the camera on.
I always charge the battery with BC-QM1 (Sony Battery Charger, as it takes only 1hr 55min instead of 5hr 10 min via USB cable). Of course I don't always put the battery back to the camera straight away. I've been asked to reset the timezone, date and time a few times only on A7 II (not A7R).
Other settings seem to be fine without the need to reset.
Does anyone know what caused this? Or do I need to send the camera back to Sony for service?