Exactly that. Roon Radio just played a track from Norah Jones’s ‘… Featuring’ album from Tidal. I thought ‘I’ve got that on disk, why can’t Roon see it?’ And went looking. And indeed it was in a folder on the NAS, and indeed Roon couldn’t see it. Until I renamed the folder to omit the leading ‘…’, when it popped up!
At a guess, Roon does something I wasn’t expecting when parsing the path.
Does anyone know? Anyone else got the album and not had a problem?
What OS is your CORE running on?
UNIX treats all files that start with a . as “hidden” so I’m not surprised it simply considered that directory as hidden and didn’t index it. Obviously, whoever named that album was not in IT and didn’t understand the problems they were causing. 
Quoted from a dev response.
Sounds like you solved part of the mystery. But, even if roon can see your local copy, radio frequently plays the streaming version instead.
Core is W10. Wasn’t in skipped files. Took me six months to notice it wasn’t there. Ripped years ago. Ah yes. Unix.
Ha! That was an ‘interesting’ thread…
I guess the NAS is running Linux; Windows could see the folder; I suspect Sonos could not until I renamed the folder. Not going to bother checking the Naim app; I turned Twonky off when I started running Roon. It wasn’t really a surprise once I found the folder.
Seems to me it’s Roon functionality rather than OS specific; I wonder if I’m missing ‘owt else?
Better go browse…
I recall I had trouble with a missing ZZ Top album. The album name is “Recycler”. With the album folder named Recycler, it was skipped by Roon. Had to change the Album folder name to “ZZ Top - Recycler” and problem solved. (metadata can still use Recycler as album name, just the folder name was a problem…too close to “recycle” as in recycle bin I suppose.)
I saw that in the thread. Made me smile… 
I have a vague memory of having to take an underscore out of a folder name ten years ago to make Sonos work… I’ve never dared put it back in case it precipitates the end of the world…
and of course the album was only part of a box set I bought that returned all the CDs to the original album mixes (not the terrible 1980s re-done MTV style drums). I only really cared about first 3 albums, but my music library ‘OCD’ required me to spend lots of time fixing an album I had no desire to listen to.
Venus orbital probe Mariner 1 was aborted shortly after launch because an “overbar” (similar to an underscore) was omitted when guidance system calculations were manually transcribed. So, you just never know. Butterfly effect and whatnot.