Some face of my mesh missing in UE4

need help, i imported my .fbx to UE4, but some face of my mesh are missing

i used Blender for 3D mesh, i already tried Ctrl + N solution in blender and Two Sides material in UE4, but it doesnt really work, still some face of my mesh are missing.

fyi, my mesh is a long cylinder that have Randomized faces

is there any other solution to fix this? Thanks!

did you checked is it flipped or not? I think those missing parts are flipped.