rear air suspension problem? Drivers rear is sitting low

[BMW DIY Guy]

Good morning all

My search-fu didn't come up with anything like what I am seeing so thought I would ask:

I just came in from the garage and had WOAH moment.. The drivers side rear is/was sitting super low, the car clearly cockeyed when looking at her from the tail. (2001 E53 btw) Regular distance tire gap on the right, clearly much lower on the left.

I fired it up, and she seemed to level herself which I think is normal, and then shut off, and can hear loud venting from both side rears, as I have come to expect as normal in this car. (its normal right?)

Is this a blown bag on the left, or something else? I am trying to find a place to start before my local shop is open on Monday.