I'm having the same problem I had last time I changed the tires on my 2004 XJ8: While I jacked up the right rear tire, its air suspension dropped. Now I can't get the jack out because the car drops as low as the jack can go (something like 3" from the floor).

I can't remember how I solved this problem last time!

The air suspension did not drop in either the front tires or in the left rear tire. Starting the engine and shifting gears did not turn the air suspension back on.

 

I had that some years ago, I just started the engine and waited for the car to rise off the jack, I then did it on each of the times with the other wheels, I was changing wheels over for the winter, as I use to do each November and back again each march.
How long did you leave the engine running while waiting for it to rise ?
Strange yours did not do it.
If not then how about jacking it up again, then putting a wooden block under the tyre so that as it lowers the car will still be higher off the ground, then carefully drive it off the block, you may find using just a 2" piece of timber might be high enough to do this.

 

Many of the newer floor jacks now have a much lower profile than the older ones.
A total of five in my shop, two are the little $59 aluminum jacks from Harbor.

 

You're right! That worked. Maybe I didn't leave it running long enough.