I see 2 problems here and potentially 3. Your car was off and one side was lowered and you jacked it up and realized it was air suspension, but the side had no air in it. You started the car and then noticed that the side which you said had no air suddenly became hard and filled with air, but you still replaced the part anyways. Now that the part is replaced you are still having the same problem and you are possibly looking to buy the same part for the other side just in case. You did not truly diagnose and fix the first problem. I don't have any true knowledge of air suspension, but the process of elimination should be used if you are able to do so. Left and right suspension are identical so when the car is off see if the side that isn't giving you problems is also lacking air, if so, air probably fills the air bag once car is started. Also try looking at the mechanical components on each side to ensure they are both functioning properly. If it's not a huge pain, try swapping the left suspected failed part to the right and see if the problem moves. This at least allows you to narrow down the problem. I would not continue to purchase parts unless you are at least 90% sure.

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1990 190E 3.0L