In reply to JRJones:
Yep exactly that across the top where the belay carabiner hits the device.
"I know I can probably rub it down with some fine emery cloth but to be honest
I am so annoyed with the wear on it after such a short time it’s going."
The above was my thought on the Reverso 3 from your comment is sounds like the 4 is the same
and from the comment on the BD above it looks like it doesn't happen with the ATC.
I expect some maintenace when using my kit but for me the Reverso 3 is not durable and from your comments
neither I suspect is the 4.