Broken mesh imported

Hello there,
Whenever I import a mesh(model) from sketchUp to ue4, the model appears to be broken, or it has some missing faces, like some walls are missing, even though ‘Double sided geometry’ is enabled
This problem was not occurring before, but from past few days its happening, also when I move a 3d mkdel from one computer to another, it appears to be broken

PLEASE HELP ME, AS I AM DEVELOPING AN OPEN WORD GAME