Incorrect lighting on procedural generated meshes

Hi guys! I’m new to ue4 and c++ programming.
I used Procedural Mesh Generation method to create models during the runtime and assigned MID on it.
And I noticed that there are some weird lighting parts on the mesh/model itself (?
Actually I’m not very sure if it’s the lighting problem. It seems some meshes are lighter than others or have incorrect lighting on it.
I have no ideas about this and struggled with it for quite a while.

Anyone can help or knows the possible reasons cause this issue?
Thanks in advance! :slight_smile: