Hi @Peter_Gallagher,
You’ve not said but I suspect you are running the Roon Core on a non-Windows platform and the music files are on a NAS.
The underlying issue is that not all implementation of the SMB file sharing protocol are as good as each other.
What should happen is the when you add files the NAS via SMB should send a message to the machine(s) that have visibility of that shared folder structure … and in turn the OS on that machine should inform Roon that there has been a change. Unfortunately with some NAS / OS combinations this is not as reliable as others. (As an aside … I use Windows 10 and a QNAP NAS and it’s fine).
To help mitigate this there is the “Force Rescan” that @xxx advised on and also there is an automatic periodical rescan that can be set (1 hour is the shortest period).
As far as I know the only other options are likely to involve switching OS and/or NAS manufacturer or using locally attached drives rather shared.
Out of interest what OS and NAS are you using with Roon?