Hello @Michael_Marchelya,
Thanks for contacting support regarding this issue. How are you mounting your Synology NAS in Roon, are you using hostname or via IP address?
If you are using hostname, then mounting via IP address and reserve that IP in your Router settings might help a bit, but ultimately we have seen these kinds of issues with “disappearing tracks” on OSX and Brian provides some great details as to why it occurs here: (Roon on macOS not working with huge library).
I hope this helps but do let me know if you have any other questions.
Thanks,
Noris