Both mine do exactly that. Still cannot find the fault. If I see the flashing leds in time, then I hit the down button and they go back to standard. Cycling the ignition immediately usually resolves it. If I have to leave it at wade height (i.e. nowhere to stop), it then faults needing Nanocom to reset it.
On mine it's usually bumpy motorways, especially where the car gets into sort of floaty up & down oscillations above 60mph. Trouble is, I'm watching the road not the height switch, so I first notice when it beeps with soft fault.