My current project is using 4.13 and I am creating an apartment type environment where I combine BSP (Geometry) with static meshes where meaningful. But the basic layout (walls, floor, ceiling) is made from BSP. There is no unusual stacking of several BSP directly on each other - just common wall / floor / ceiling layout.
From the beginning of the project I am facing various forms of BSP rendering problem that have common symptoms:
BSP become either INVISIBLE or only partly rendered
BSP loses its MATERIAL information on one or more faces.
Some actions or property changes can cause editor CRASH - there should be several crash reports sent from me around 17. - 18.9. 2016. E.g., Order change of the incorrectly rendered BSP caused crash several times.
These problems makes using BSP practically impossible and I assume the only solution is to replace all BSP by static meshes (or to try another editor version) unless there is a trick to go around.
I have faced several different stages with above symptoms:
A. In the beginning of the project I created one big floor BSP but at some places I needed a different material so I created a thin BSP (width 0.2) and placed them directly on the floor so 0.1 unit of the thin BSP was above the floor level. Very soon some new thin BSP were not rendered correctly.
(1) One thin BSP makes floor transparent. (2) When I dragged the BSP up and increased its size the rendering problem was still there but when it was high enough above the floor, then BSP itself was fully or partially invisible. (3) This one just lost its material.
Here one BSP was partially rendered.
I managed somehow get over this stage by playing with BSP Order First/Last → but that in some cases caused editor crash.
B. Later I noticed that when I build geometry / lighting or just create or copy a BSP, then some BSP faces lose their material (I guess around 20 faces material losses out of 100 - 200 existing BSP faces).
C. Last and terminal stage is when by practically any action (building geometry, lighting, placing BSP, deleting BSP) (I guess) all of BSP become incorrectly rendered:
Above: before any BSP related action …
… and after.
For illustration I have selected one invisible BSP. Remaining visible objects are either only partially rendered BSP, BSP without material or static meshes.
Please let me know if you find out any temporary solution other than static mesh conversion (which I will probably do soon to be able to continue.
Reproducibility: Well, it is hard to say. There are posted several similar issues on this server (both old and new). I would need to start a similar project to see how reproducible it is. The first stage was just a few BSP so it might be doable. On the 4.12.5 I am doing very similar project but I have not seen such a problem all along the project. There were only some special strange rendering when I used transparent materials there but this is another story.