This topic should be made a sticky because I don't know how many times I have answered it .

What is happening exactly when booleans make geometry dissappear?

There are a number of reasons that can cause this.

Check the script editor, it can tell you most times what the problem is and how to fix it.
If the Script Editor is no help:

Things to check to make a successful boolean

1) Both pieces of geometry must be intersecting completly, even one vertex that is not will cause a problem.

2) Always make sure that there is no
nonmanifold geometry around the boolean operation .

3) Both pieces of geometry must be closed meshes. and by closed i mean every vertex merged.

4) Check the normals on the surfaces. all the normals of both pieces of geometry must point outwards or inwards but most importantly the same way.


That is more or less all situations where you can run into a boolean problem.Intersection, non-manifold,closed mesh and normals.

I would avoid Booleans myself as it can make a mess of your edge flow and you almost always have to clean it up afterward.
A better solution IMO is to draw out the cut with the split polygon tool and delete manually and merge the two pieces yourself giving you much more control of the operation.