There is a related fix in the V10 daily builds:
"CoronaScannedMtl assets are now tracked via the asset tracker"
I guess the workaround for now would be loading the Scanned Mtl from a network location and making sure that the render nodes can access that network location. I am not aware of any other solution, sorry.
If this is very problematic for you (you cannot continue working because of it) - please do let us know and we will investigate further.