Title tells it all. The CSG geometry support has never worked correctly in the UE4 editor … at least not in the two+ years I’ve been working with it (4.5). It still suffers from missing/mutilated geometry when building levels which suggests the csg compiler is borked. Even simple geometry like a basic wall is a **** shoot whether it’s going to compile correctly or not. Granted BSP brushes are old school. But there are times when you need a simple one-off construct that just isn’t worth getting the 3D modeler out to create (not to mention filling your library full of one-use models).
Can you show an example of BSPs not working fr you.
Admitted, I abamdoned BSPs a while ago and use static meshes for blocking instead, but when working with them I only had problems when using a lot of them…
I dont think BSP related bugs will get a high priority. Probably a “wont fix” right away.
Dont forget, there is still the GeometryEditor 2.0 just beyond the horizon 
Then its maybe a problem with your cumbersome modeller 
For me, MODO does a very good job 
Rumor has it this problem is fixed in 4.13. (ref: UE-12157, UE-35290, CL 3072169). I will try to apply the changes to 4.12.5 tomorrow and see if they will work or if they have some additional hidden dependencies.
I applied CL 3072169 to 4.12.5. It does not fix the BSP problem.