It seems like it’s entirely impossible to get chunks to have an interior material in 4.20+. I’ve tried with a plethora of different meshes and they all yield the exact same result.
Upon fracturing a mesh, it does not create a 2nd material for the interior. And if you add one manually - it is never applied. Trying to add a third material and then fracturing results in the editor crashing.
Now it seems as if the Material #0 is forcefully applied to both exterior and interior material slots. This is terrible.
This seems to be working as intended in 4.12.5 and
If anyone knows of a fix or a workaround - that would be greatly appreciated!