So, When you had the Roon Core on a different PC you had to setup a share to the zen for that PC to access the music.
However, the zen itself sees the music as an internal folder NOT via the same share that the other PC had to use to access the music. In the screen cut above, you see that the Zen is now seeing the music on itself in the Music Folder.
Now, if you notice below, you see listed the “zenmini > Music” storage location, that is the share that Roon used on your old PC. And that is the location that the music files meta-data is tied to.
Notice that under the listing it is saying the drive is not available and then followed by an “edit this folder”. You need to edit the old share to point to the internal music storage.
So, first DISABLE the current Music Folder. THEN, click the “edit this folder” and choose the new internal location of the music on the zen. After a quick scan, everything be back to square.