I thought this was a bug with 21.1.2, but I have since installed the previous two windows builds back to 20.2.5 and its the same. It could be Maxon but its a pain regardless. Materials stored in the Local DB cant be relied on to work correct anymore. Within standalone the materials display a bit odd in the selector(greyed etc) but render as they should, however the same material from the same place when pulled into C4D corrupts something. I have a video linked here to show exactly what is happening. Using C4D 25.117. It seems to effect the metallic materials mostly from testing, the materials were an older silverwing pack.
https://f.io/y8f5IWp9
Regards