Hello, hello!
I’ve been pulling my hair out all afternoon, until I found this thread 
I thought I must be doing something wrong, but it looks like it’s actually just really, really buggy right now?
Just posting here to keep the thread alive, because I can’t get WP to work predictably at all.
I tried WP in 5.0.3, creating a new map and converting an old map. Tried the same thing in 5.1.0 preview. Always the same results.
I basically just create an array of 1m cubes which sit on an array of 30m planes.
Everything streams in an out unpredictably.
Some cubes remain visible the entire time, same with the planes… Just won’t cull.
When I start moving, random planes and cubes pop into view, even way beyond the distance I had set. I move backwards, some won’t cull anymore.
Lighting setup I had done via Env Mixer won’t load at all after play start (neither ingame, nor in editor after exiting), needed to use the little pin icon to get them back.
The world partition mini-map display is also breaking for me in 5.1.0, permanently displaying the click/drag selection outlines (when trying to select regions to load in) etc etc.
Oh and sometimes the editor crashes altogether when I try to view the 3D debug. 
In this state I find WP totally unusable… but it really seems to work ok for some people. Any thoughts at all why it works for some users and not for others?
Nonetheless, great stuff, love UE 