I searched and noticed this is a 2 year old bug, but it is still not fixed in 4.11.
The bug is as follows: re-importing LOD meshes separately in the static mesh editor stacks materials by importing a new material without overwriting the old one. I haven’t tested yet to see if this actually affects draw-calls but I’m guessing it probably does, as the mesh reports that it has many more materials than it actually does.
If it is purely an editor error, it’s just a little annoying, but if it also affects the game at run-time then it could pose issues for mobile or VR games with a tight draw-call budget.
I did a quick search for the issue you mention, and it is still Unresolved at the moment. We have added a lot of community interest tied to the bug report UE-1394, and I have marked it to be looked at again. Once the bug has been addressed and a fix is made, it will be added to the list of known and fixed bugs for an upcoming hotfix or major engine release.
Let me know if you have further questions or need additional assistance.
I’m getting this in 4.27. I imported my mesh and set up the material elements. Then I imported the LOD and it doubled the material elements instead of using the existing ones even though both the mesh and the LOD are using the same material inside 3Ds Max.