I have had some/many objects doing this. I think it has something to do with the vertexes. Sometimes they just have a position that the boolean/slicing function wont work with. Of course it can bee some other thing as well, but its just guessing from my part. What I do to resolve this is either move the knife slightly, or, a bit dependent on the object, do a divide on selected surfaces. difficult to say when not looking at the object