Cars generally have a set of protocols that shuts down the entertainment and other systems to avoid the car’s battery going flat. If, for example, you were listening to the radio without the engine running, eventually, the car would switch the radio off to maintain the charge in the battery.
It’s quite likely that the message you’re seeing is something to do with this process. Why doesn’t it send the message every time? Perhaps it only does so after short runs where the battery isn’t fully recharged after starting the car. Maybe your battery is starting to feel its age. See if you can find a pattern to the message appearing; short runs, cold weather, wet weather, air-conditioning on or off, etc.