Applying Union Boolean to vectors of Icon breaks the icon.

Hello Everyone, idk why but for some icons when I try to unify the vectors it break the icon like some part of the icon disappears idk why

Here is the icon before unifying vectors inside it

Here is the icon after unifying the vectors inside it to form a single shape

As you can see it completely changes the icon. Idk why this happens but this happens for a lot of icons but not all icons.