So my current feeling is, say if you have 5 material networks, 50 sop import nodes, and a chain of 5 material library nodes, it is very likely for karma to mess up with the sequence of assigning materials. And, the tweaks of material is not going to trigger an automatic IPR-restart, you have to unlink the material library node to trigger the restart.

Here's an example.
1.Prepare a Lab's luiz in /obj content
2.Create a material builder contains a skin shader core in stage/materialnetwork, as well as a principle shader
3.Use material library to assign skin shader core's material builder. Karma renders correct image
4.Add a blank assignment that only fills in the principle shader but not the geometry.
5.Karma puts that principle shader on Lab's Luiz geometry.




Sometimes, you have to unlink and link for several times before a IPR-restart happens. When you pause rendering and restart render, the materials update is not showing up. sometimes after few minutes when you are not updating the material, the material update you made in dozens of minutes ago triggers the material update....In the aforementioned example, the material update of assigning an invalid geometry happens minutes after my operation on the material library node.

There might be a bug here (maybe the blank assignment is actually assigning to "/" with a strong opinion?), not sure. That said I'm not sure it's a good idea to handle the material assignments directly in the MaterialLibrary node. The AssignMaterial node gives you a lot more control, including control over the "opinion strength" of the assignment.