Replying to this thread because i found it on Google, while researching the same problem. If someone like me stumbles here too, there is a solution. What happens: somehow maya locks default shading group node, this prevents material assignmnts and, by extension, creation of input nodes for poly primitives. What you need to do: Unlock default shading node Mel command to unlock initialShadingGroup: lockNode -l false -lu false initialShadingGroup; This problem is present up to Maya 2019, maybe even later.