Do you have the latest RoonServer package installed?
Does it not work for you? Then please post more information:
NAS model
DSM version
Roon Server package version (release date)
And while you wait on a further reply, a user also posted a workaround (before the package with the fix got released) that might still help:
PS: Think about adding an UPS to your NAS. A sudden power failure may damage Roon’s DB and the usually required filesystem checks after may take hours (depending of the amount and speed of the installed storage).