[Paul T]

Originally Posted by craigster59

Surfactant leeching. In other words, paint additives leeching out and dripping down the wall....

https://www.sherwin-williams.com/en-us/project-center/maintenance-repair/surfactant-leaching

Interesting, thanks. Looking at the pattern though, it sure appears like this "leak" or whatever it is began at the top and oozed down with gravity....that's how it appears to me at least.