I am embarrassed to say it, but I now don't think it was the upgrade.  I purchased DAZ MadLab 4, and after installation moved the folders into a central folder because the installer put the characters in a lot of folders - never had a problem with that before.  I moved the folders back where the installer put them, and now things work right again - so I uninstalled the MadLab (the props couldn't find their textures anyhow) and am going to complain to DAZ.  In 7 years, I've never seen that reaction to moving folders, but probably something tied to the installer.  Oh well, live and learn.