Hello Jamie,
I have the same problem. The rescan only work sometimes. Mostly I have to manually rescan the folder.
My machine:
Synology 918+, DSM7.0, latest RoonServer by C.Rieke
MacOS Catalina, latest Roon v1.8
By the way, I can not find “Automatic Rescan Interval” in my settings. My storage setting looks like this. I tried scrolled down, but there is nothing below “Ignored Paths” setting.
thank you,
Yasmina