HLOD generating corrupted meshes with 0 triangles. What are some reasons this may happen?

Fresh levels seem to work fine for the assets that typically cause problems in that main hall level… likewise if i move those assets to a new level via level browser or even copy them to a new level… same problem … 0 poly … corrupt meshes etc etc…

One of the assets was the broken plate model causing a problem, but if i throw that model in a fresh scene drag and drop… it generates fine… So it has to be level specific… But why?

I did use a lot of group nodes and scaling… and parenting + scaling +unparenting… in that level… not quite sure what else could be causing the problems…