I run a MU WordPress with several websites. One day I noticed that I was unable to add roles to the people on one of my sites. No matter what I did couldn’t get any roles to appear in the selector.
Some how in one of my updates the prefix for this particular site wasn’t updated. I found a post telling me this:
Following this line of thinking led me to change that particular database table name. Sure enough renaming the table worked!
Previously it was named wp_89_user_roles. It needed to be named 64d_89_user_roles.