Weird shadow effect after slicing procedural mesh


i’m relatively new to UE4, i’ve been trying to create an object slicing tool, i’ve followed few tutorials including the Procedural Mesh Slicing video from official UE youtube channel and made a few changes.

The slicing works great, but after slicing, there seems to be sort of “ghost shadows” where the sliced part of the mesh used to be, they are visible only from certain angles.

Does anyone know what’s causing them and how to get rid of them?

Thank you in advance!