I think I have the same problem see: my topic here
I think something has changed either in Mac OS or in the NAS frimware. In my case I also suspected something was wrong with caching of the share name (In my case //NAS4/Music) so I shut down Roon, renamed the share name on the NAS, started Roon, removed the storage location in Roon, restarted Roon and added the new named folder as storage location. After that It started scanning but after about 300 of the 32000 tracks it stopped completely and also I could not access the files through finder anymore,. A computer restart fixes this. If I restart Roon after that error It will say something like share or network not available.
This pattern repeats itself with every thing I have tried in the last 3 days. After a lot of tries I can get it to start scanning the music folder but It will always freeze the number of scanned tracks at a certain number and than nothing happens, not in Roon but also not in all other Osx software. If I do not start Roon there is no issue with accessing the Nas.