Rear Ride Height issue dealer can't figure it out

[Jim M3]

I bought an X5 about 2 months ago and the first week I had it I noticed in the morning the ride height would drop to the bumpstops. The dealer kept it overnight and tested for leaks but couldn't find any in the airbags, they tested the compressor and decided their must be a leak in an air valve, so they replaced the compressor assembly.

This morning the X5 is back down on the bump stops even with the new compressor. This system doesn't have a lot of parts so it is very difficult to imagine where the issue is, I wonder if it is with ride height sensors? But why would the system deflate overnight if there were no leaks?

Any thoughts, I just got rid of an Audi Allroad because it had air suspension issues only to get an X5 with similar problems. I have an E53 and have never had one issue with an airbag or pump.