I went through something similar until I got exactly the right match between the specific directory I was sharing and the one I used in that setup dialogue in Roon’s.
So what happens if you
- remove the share completely
- create a new hierarchy - outside ~/Music - just in case Roon is confused by the option to have that as your default watched directory: say ~/RoonBackup
- set that up as your only share
- in the Roon dialogue use:
- smb://RoonBackup
?