The message is displayed after launching Roon (Windows 10 PC). The album is available, e.g. it is possible to track it back in History. Network connection is OK.
If it used to be on one of the two services Tidal or Qobuz, it doesn’t have to be there anymore. Sometimes it was just switched to HiRes or another technical reason leads to a new link. If the artist doesn’t like streaming anymore, he leaves you alone with the problem and doesn’t release it.
It happens consistently for all albums, no matter if they are on Tidal or on local LAN NAS.
NAS, internal SSD, USB-HDD…?
Two sources: NAS and Tidal streaming. Same behavior.
Then the paths to the library are lost. Search with the keyword QNAP, there most problems were described and with (partial) solutions. I think there are more solutions sought, but I have not pursued that I have only USB hard drives and no NAS. There was a switch from Mono to .Net, new security updates at QNAP and Synology and much more…