From a technical standpoint size of the library doesn’t matter in this case, what matters is the architecture of the NAS storage - RAID, non-RAID, RAID 0 or RAID 10, is NAS in sole use of Roon, or other system is draining the unit – such as Plex, for instance. On top of that, if your router has issues or had been previously troubled with such protocols as UPNP (even though Roon uses it’s own proprietary RAAT), there is a huge chance of potential issue.
I’m not arguing with the fact, that you system works perfectly and I’m glad it does. The problem is that YMMV from what the majority or at least some about of users currently or used to have. And as I’ve pointed out previously to the link above, there are better and more efficient ways.
I’ve had Roon for several years, and I used a Synology NAS for music storage until sometime last year. The two main issues with the NAS setup were that, as reported, the network share protocol does not propagate NAS updates automatically, and in general slower local music search and retrieval at the start of an album. Since my local collection has a moderate size (1700 albums, 1.1TB) and I have full control over the ins and outs of the NUC running Roon Core, I moved music storage to a 2TB SSD on the NUC. As a Linux geek, I’m happy to download or rip new music to the NAS and then rsync it to the NUC SSD. Not any more convenient than asking for a Roon rescan of the NAS after adding music, but performance is significantly better, and I’m sure I have two copies of everything just in case (I also do cloud backups for the Roon library and all downloaded music, and HD full backups of the NAS to be safer).
There is a degree of ‘it depends’ here. I’m using NAS storage, configured as network share, and Roon picks up changes immediately. Sometimes too immediately. It’s an old drive and it’s slow - when copying in a new album, Roon will occasionally identify a partial album and I end up with tracks split across that and several ‘unidentified’ albums, followed by fun with the merge tool. If I remember in time I’ll disable the storage/copy/re-enable.
Why? Don’t know. Maybe because it’s using an old protocol.