Mark,
I can load the file just fine. Normally one can see a colorful triangle when a material is on a layer, but if that layer is gray, it might be hard to recognize.
A substance couldn’t be loaded, no idea if that was the case, I don’t think so that this caused the trouble.
I exclude as well the use of XRef here as the little x in the lower corner doesn’t show up.
All textures were naturally missing, but since it didn’t grayed out here, I do not think it was the problem.
A rough representation of my exploration is here, just a sketch:
https://www.amazon.com/clouddrive/share/4qdKDlSaXHNyZjgn9ybQqSashsNFrlewIMEv8hZ3bt0?ref_=cd_ph_share_link_copy
There are three options:
Create a layer and place them onto the new layer, if they had a layer at one point and the file got buggy this might heal it. Perhaps see what happens if you go to Material Manager>Function> Render all Materials, you will see that they get temporarily grayed out. Perhaps they got stuck doing so before.
Select all (in the Object Manager and copy it, open up a new scene file and paste it.
If both option do not work, check with the Support:
https://www.maxon.net/en-us/support/how-can-we-help/
All the best