Need help with the physical starlight atmosphere add-on

I purchased and downloaded the physical-starlight-atmosphere-1.5.2 add-on a couple of days ago and while the sky and light effects in the scenes are quite impressive, the rendertime has doubled… something that I can live with, but what alarms me is the following issue that has occured three times by now:
I sit and play with the addon settings and suddenly when I press “activate fog” certain buildings instantly lose their material - in the material view port preview as well as when rendered. Most buildings keep their material. If I save the file, the problem remains when I open it again, so its not some temporary memory issue. Ive worked with Blender since 2009 and I´ve NEVER seen anything so weird, thats why I ask for Sherlock Holmes to solve the mystery. - because I really need that fog effect.

On their website the makers

literally put a link to BA :

A post was merged into an existing topic: Physical Starlight and Atmosphere Addon for 2.9 (v1.4) - now with Clouds!