R300 Airmatic - issue or normal?

Hi, have had my Merc R300 for about 6 years now. 8 months ago it was rear-ended and repaired. About 4 months ago, periodically, overnight the rear suspension (Airmatic?) would completely lower. It comes back up once the car is started, and there are no other warning messages etc other than to wai whilst the heigh is being adjusted, but as this never occurred prior to he accident I'm concerned that something did get damaged as part of the accident?

 

It happens irrespective of whether it is cold or hot, typically only after the car has not been driven for 2 days. Thoughts?