Problem to render cylinder and sphere using Assimp library from Blender

I have problem to render .stl model using Assimp library: if I create a cube on blender I can export it in .stl and import in OpenGL using Assimp without problem, but if I try same thing (same position, dimension, rotation) creating sphere or cylinder, rendering in OpenGL is not correct (cannot see entire model only some portions).
Could you please help me?

Thank you