Hi everyone I am Alan new to MF

I have a UK spec E350 W212 saloon 2011 model and recently took the car into a Kwik Fit to have compressed air taken out of the tyres and replaced by Nitrogen (I swear by Nitrogen its much quieter on the road no tyre roll less slow punctures less variation in pressure when weather gets hot etc.), in doing so the car was sent up in the air on the type of ramp that leaves the wheels free, hence suspension goes to full drop, since this job was done I have noticed that when the car is stationary for a few hours or overnight the height drops on mainly n/s rear, no warning lights come on when the car is started, and after a few seconds the car rises, occasionally a message comes on the dash that the car is rising but not always even though it does rise. Should the car have been started up whilst still in the air before it was lowered back down on to its wheels? or is it too late now?