Thanks for the quick response. I suspected the Logitech G-Hub drivers myself but I'm not seeing any odd behavior in other apps like Windows' File Explorer where a stuck control key would be obvious. The on-screen keyboard doesn't show any of the ctrl, alt, fn, Windows keys as being pressed.

Oh this is weird -- after I brought up the on-screen keyboard and closed it, the endless renames stopped. All is well.

I'm definitely going to put this down to G-Hub misbehaving. Thanks again.