I created a new sub-folder for my UDTs and moved a couple UDTs. After performing the move, of course I was expecting to have to update the UDT path for the affected UDTs. However, every UDT that exists in my tag provider shows a configuration error, even though when I open the UDT instance definition it points to the correct UDT path.
To resolve, I've been adding an "s" to the end of the path, apply the changes, then remove the "s" and apply changes again. This makes the configuration error go away, but I did not expect this to affect other UDTs that are completely unrelated to the ones that moved.