Hey McGreed,
I was able to import a mesh with LODs and Custom Collision without any issues. My workflow was a little different though.
After I set up the LODs for the meshes I then modeled out the custom collision Geometry and gave it the UCX naming convention. I didn’t add it to a group or attach it. If you would like you can send me your FBX or MAX file to test with to see if I can reproduce the issue on my side. You can PM me here: https://forums.unrealengine.com/member.php?484739-Ed-Burgess
Also here is the FBX I tested with.
Regarding the other issue you mentioned would you mind making a separate AnswerHub post for it as others who are having that issue will find is easier that way.
,
Ed