Ugh, got caught up by this as well and spent a good hour trying to figure out why it wasn’t working. Setting mesh to movable indeed solved issue.
What still doesn’t seem to be working though is assigning a material at runtime to this mesh with SetMaterial. mesh keeps rendering with default grey checker pattern. Any idea what to do there?
Edit: Never mind, just found out here that materials need to be explicitly enabled for use with spline meshes. Therefore this is now working as well.