I was able to fix it, rather easily, but I’m pretty certain the fix isn’t what you have in mind. I logged onto my MacMini, stopped Roon Server, restarted Roon, and it found the missing album within a couple of secs.
Please recall that I reported on a different thread an issue where Roon Server can’t re-find my NAS after it shuts down in the evening and restarts the next afternoon. You said a fix hopefully was coming in the next Roon release. So until then I now keep the NAS running 24x7. See Content isn’t added when NAS wakes up
So it appears right now I’m broken if I keep everything running (when adding new albums) and broken if I shut things down (putting server to sleep) - Damned if you do, damned if you don’t. At least I understand the problem and have a work around. 