Oops!! Looks like I jumped the gun on this one.
It started working after I deleted the C9 preferences folder but now it’s back to not renaming things.
A bit of digging showed this post: Double-click Intermittently Works in Cubase 9 / macOS
This is exactly what is happening to me. I’m using a magic mouse on a mouse pad. Double clicking just doesn’t work. However, if I move the mouse to the desktop and double click it works fine. Lots of people seem to be having this problem … only in Cubase on a Mac.