Hello! So, I can’t teach myself to use any editing software. I just cant use them.
I am building a game and I wanted to do a signal for a train (just design wise, not functional) and I made it using a 4 cylinders and a super awkward sphere. The thing is, the geometry bugs out when close together. (I updated my GPU drive just so you know). Take a look:
This is a simple cylinder from Unreal Engine. I do not use Blender as I don’t really know how to use it.
And I tried to remake the cylinder, but when I put it there, it just bugs out. In other places it is ok, just not near other geometry.
Either these faces are missing or if they are just visible from one side, then the Normals are inverted. If you are using blender to make your Assets: Go in edit mode and press ctrl+N to let blender calculate the normals again or press space and search for flip normals. Flip the normals on the affected faces. There also is a Check box to render the backface Culling in Blender in the the right panel of the viewport (press N to show the panel), the checkbox is under the ‘Shading’ tab.
Mark this as an answer, if this solved you problem (under the rating of the answer should be a check)
Oh you work with the Geometry Brushes? Geometry Brush Actors | Unreal Engine Documentation
I can recreate this with 2 cylinders of very close radii like 200 and 199.75. It is not expected that the geometry is perfect with these tools. They are nice and easy for creating a rough world and these Bool operators (Additive and Subtractive are the two brushtypes) are not always that clean, even in 3D Modeling software, especially when the Geometry gets more complex.
You should make it more rough or look into modeling software, like blender 
