Hi Sagda, here is a version of your object that has been repaired to get rid of those 3 little unjoined edges to make it back into a solid. Booleans should now behave as expected again on this one.

So one thing to watch out for is try not to make curves that are almost tangent to each other but only off by a few degrees. That kind of very shallow crease will tend to make it difficult to fillet later on.

- Michael