I’m still digging into World Partition. I watched one of the Youtubes on the Unreal channel for some clues: New World Building Features | Inside Unreal - YouTube
What I did this time was created a data layer and assigned my landscape streamers into it, saved, closed down then opened back up. Things are working more smoothly, but I have not tried landscaping again for fear of massive lagging. I suspect assigning one quadrant to my landscape per data layer and turning off Lumen may speed things up, but it was pretty heavy operations last time I tried.