X5 E53 3.0 Rear right suspension down in the morning

[hellgrace5]

Hi.I noticed my car's rear right air suspension going down in the morning. It happens very rarely. Like twice a month or so.I put it to a scan and it came up with no fault. I noticed that the rear right solenoid valve has no voltage supply.No fuses are blown. Recently just replaced the left rear leveling sensor because dash warning says air suspension inactive and it was solved.What could cause the problem?Thanks!