Hi Jeffery,
I had a quick look at this, and I am seeing that the Niche Side and Back are not applying the material to the sides of the niche. I think this is an adjustment to the way the walls are created in V17. I will have development look into this. However, in the meantime, you can assign the material you want by adjusting the Wall’s Appearance Properties for the Core Surface as shown below.
Hopefully, this helps get you what you are looking for.
Thanks,
Nick
