Background lighting - Ambiental lighting

[Versace]

I've had this unusual occurence... Driving on the motorway, the Ambiental lights in the door cards - the long ones just stopped working, than in few seonds came back again. Than again in few minutes they're off for good. And I don't know what to do to turn them on again. Every other option in the Background lighting works (City, Back, Front) only "Highway" lights on the door cards does not work. Where should I start looking for the solution? I have VCDS...