That kindof looks like degenerate geometry being culled out.
Degenerate triangles are when the faces are too small for UE to handle them well. If you get an error when importing about x object has degenerate triangles, that would be the problem. It is usually an issue with scale. Since blender is set to meters as its default scale instead of centimeters things frequently come in too small. Changing blender units to centimeters and unit scale to 0.01, checking to make sure the object is the correct size and then applying scale in blender should help. (you will frequently have to scale up by a factor of 100)
Datasmith rinses models before import, so that might ignore this issue.
I wrote a plugin for this
And there is one through epic games as well:
Both are free
My use cases are for film specifically but should translate into the games sphere as well.