Hello, same problem here, though I figured out when and what broke it. So yesterday I tested the Water System and added a River. After it, I started to experience that the World Partition doesnt work anymore on landscape cells (though still works with foliage and external actors).
Fortunately I was able to restore my prev content and lost only one day work.
But it does mean for me, that Water System for WP is still a big no go. 