I have a similar setup, same problem. The easiest temporary workaround that does not require a NAS reboot is to go to the “Connected Users” widget and kill the frozen CIFS connection(s) from Roon Core by clicking on the (-) (wrong way sign) icon. Roon Core then reopens the connection and everything works again, for a while at least. My hunch is that the connections freeze when the NAS hibernates because the new Core software is not handling occasional latency/timeouts properly and marks the connection as not ready rather than retrying the connection.