The problem is that the tyMesher combines all meshes, so the only way to assign multiple materials to it is through a multi-sub material. Now, in the past some plugins allowed you to auto-combine multiple materials into a giant multi-sub material (ex: XMesh)...but with a variety of renderers all offering their own multi-sub style texmaps now, doing that is no longer possible without messing up those maps.
So the solution is to manually set the proper material IDs first and arrange the multi-sub material layout ahead of time, so that when all the meshes are attached, you can just apply that multi-sub material you previously setup to the tyMesher. Automatic conversion of multiple materials into a giant multi-sub material is no longer possible without potentially breaking a lot of the maps assigned to objects.
So the solution is to manually set the proper material IDs first and arrange the multi-sub material layout ahead of time, so that when all the meshes are attached, you can just apply that multi-sub material you previously setup to the tyMesher. Automatic conversion of multiple materials into a giant multi-sub material is no longer possible without potentially breaking a lot of the maps assigned to objects.