In our experience assets with multiple submeshes currently produce an assetbundle with only one submesh after the asset is loaded.
This didn’t use to be the case.
I have more specific info but not a general purpose test case yet. It appears that if the asset has a group with a mesh under that group that has multiple submeshes, the lower level mesh is in the asset bundle but is set to inactive. In the case where there is no hierarchy and the object is just the mesh, only one of the submeshes is preserved.
In the case where the lower level submesh is inactive the top level is active but only has one submesh.
This is with using sketchup files directly (submeshes totally broken, no workaround) or with fbx export from sketchup (top level object broken - can workaround by activating lower level submesh and some renaming tricks.
Here is an example of an FBX from our project that has this problem. All meshes and submeshes display properly when it is used directly after being imported. When we build an asset bundle and load this at runtime, only one submesh is included and displayed.
2503529–173080–smallMetalTable.zip (17.9 KB)