Boolean operations between Brep entities don't work well in case one of the two Breps has an edge or a face tangent or coincident with an edge or face of the other Brep.
If the coincident faces are planar, most cases already work in version 12. In version 2020 we increased the number of supported situations.
In particular, we can now perform some boolean operations between Breps A and B also when a cylindrical face of A is coincident or tangent to a cylindrical or planar face of B.
There are some limitations, that we hope to overcome in the next releases. The images below show some examples of boolean operations that we started supporting in Eyeshot 2020.
The red Brep is A, the blue one is B; each row has in violet the differences A-B and B-A, in green the intersections and in beige the unions.
Now the following geometry can be built in Eyeshot: