The display functionality to show the serial number can be triggered by dust which accumulates on top of Somnofy.
Some customers experience a problem where the display scrolls through the serial number and firmware edition continuously.
This is a "side-effect" of the functionality which is triggered by holding the hand over the top of the unit for a prolonged time. If the message now scrolls constantly, the sensor on the top might be blocked by dust or something else.
Try to blow on the top to try to remove any dust or particles, and use a soft cloth to gently wipe the top. This should solve your problem.
Do contact support, if the problem persists.