DIAGNOSIS The internal backup battery on the main control board is dead or disconnected. This is a common failure point after a few years.
FIX There is no user-replaceable battery. Plug the machine into a working wall outlet and do not unplug it. The clock and settings will maintain as long as it has mains power.
IF THAT DIDN'T WORK The issue is a faulty main control board. The non-volatile memory chip has failed. This requires a board replacement.
HEADS UP Using a smart plug or timer to turn the machine on/off will cause the clock to reset daily, defeating the auto-start function.