It turns out that I was probably affected by the same issue reported in Dropouts when streaming via Roon to NAD C 658
For whatever reason my NAS stopped sharing the music folder and only that since I installed Roon, I didn’t give it much thought because with Roon I was not using that but the NAD clearly has a problem with that. I reactivated the sharing and the system has been playing without interruptions for one hour, I hope it stays like this 
Now I feel bad for not having found that thread sooner 
I guess I was thrown off track by the fact that streaming to BlueOS directly worked perfectly. I hope this can help other people in the future.