I know, I just can't keep away from the much maligned Roombounds but their usage is a necessity. Allow me to explain the predicament:

Just created the final dungeon for my mod. After much blood, sweat and tears I'm nearly there! It's done in a WorldSpace because I needed some land to play with. Now, if I set the WorldSpace to "Fixed Dimensions" a couple sections of the dungeon disappear as I presume they are outside of the boundaries of a fixed dimension worldspace (..?). If I untick "Fixed Dimensions" the entire dungeon appears which is great however the land disappears instead! Strangely enough I can still see the stones and grass associated with the land textures and the collision is still there ... just not the texture itself!

Now I know Roombounds don't play all too well with WorldSpaces without Fixed Dimensions ticked and the Creation Kit raises a few warnings about this configuration, however judging from my play testing the Roombounds still seem to be functioning in this state. I just have no idea why the land is disappearing.

Has anyone encountered this before?

If no fix or tweak is available I suppose the workaround would be to copy the entire level to a standard interior cell and use dirtmound objects instead of a real ground, however I would need to rebuilt the navmesh ... something I would like to never do again. ... for now at least.

Roombounds and worldspaces are a no no.

Roombound optimise interior cells. LOD optimised exterior worldspaces.

Use occlusion planes if you want to optimize in an exterior. Bethesda added a huge collection of occlusion planes under Solitude to optimize it.

Not sure why they're considered a no no, there are many worldspaces such as the Labyrinthian worldspaces that use roombounds, though those levels seem to constrain to a 3x3 cell radius around the center cell hence the reason why Fixed Dimensions doesn't chop any of the level off. I suppose I should just redesign the level slightly to keep it within the 3x3 radius... but I'm too lazy.

Decided to move everything to a regular interior cell, the dirt mounds don't look as nice as proper land but I guess the most we can do is work around these unusual limitations.