Problems with moisture in exterior plaster

That is probably true. ;-) It cost me some research and analysis to find all this out. Thanks to this incident, I am no longer a layperson when it comes to external plaster. I just don't know what to use the acquired knowledge for, as I probably won't be building another house. :-D

I just don't know what I can use the acquired knowledge for,

I think what you wrote down here is already very useful and very easy to understand. So, a thank you from me for that! And great that you also report afterwards how it turned out. :)

Also check what weather conditions prevailed at the time of applying the plaster and painting the facade. It may already become apparent that the external conditions were fundamentally wrong. In addition, there are defined waiting times, for example, between two facade coatings. I actually had to insist on this during the defect rectification, as the executing company would have otherwise ignored these defined waiting times again.

We also engaged a construction expert to reinforce our position and the demand for defect rectification. Although we ultimately bore the costs ourselves, as I did not want to fight this any further, it was worth the money.

We were completely satisfied with all other trades. We have now been in our own house for more than three years and enjoy it every day. :-)