I'm now on my 4th Surface Book. All 4 have done this.
I hope this bug is on the Surface Firmware team's TODO list too as it prevents me from enabling the auto-switch to tablet mode option. If you turn that option on, instead of just the "Auto Rotate On" message, the computer randomly switches into and out of tablet mode all the time.
Super annoying as the auto-tablet mode switch (supposed to only be triggered when you detach or reattach the screen) is one of the biggest selling points of Windows 10 and the Surface line.