A problem about flat model

I tried to unfold the global earth into a flat model by used the GeographicProjection file,just like this.

But unfortunately, When I try to align the coordinate system with UE’s coordinate system ( by change this function:UCesium3DTilesetRoot::_updateTilesetToUnrealRelativeWorldTransform) , Terrain tiles flicker very badly and as soon as we select the “World terrain” in editor, flickering stops. (just like two pictures at the end,Reciprocating refresh).
By the way, If I don’t make changes, it won’t happen.How can I solve this problem? Thanks in advance.