Roon always rescan the library

i know this is not discussed the first time …

ok - my setup
i have two locations where all my music is stored in the network at home.
1st is a synology nas (main)…2nd a internal harddrive of my mac pro (here is the music before everything is proper tagt with cover iso to dsf and so on…)

roon core is running on a macmini connected with usb regen to a mytec brooklyn.
all is connected with cable and static ip´s and smb protocol.

when i restart the mini and so the rooncore - roon is re scanning?
and its re scanning by itself from time to time? and with re-scanning i mean from point zero…so it starts with no music and is not scanning in the background looking for more new music?

any idea…of course i tried i only with the nas…same problem