Meshes that are going to be setup for destruction work best when they have been setup in a specific way for their edges. While I can see in your mesh that the everything has quads that can be triangulated, it doesn’t react well with DMs. By adjusting some verts and stitching them to other verts there is no loss of geometry definition, only removal of extra faces.
I wanted to update on this issue. The engineers have decided that this issue will not be fixed. While in-editor fracture tools will be improved it cannot be guaranteed that they will always match that of PhysXLabs. Using the methods previously mentioned as a workaround will be the route to go with correcting the issue with UE4.