I have an album that is had ripped from cd and added to the library. It shows up with the book icon. But there is no download arrow to access it offline:
That’s because the version viewed is on Qobuz. Visit the Versions tab, and the local copy should be listed. You can change the primary version using the Roon Remote app.
For Local Hero there is no version tab. I am also having a problem with this album and I am selecting my library version but no download arrow. All my other albums I have wanted offline have no issues, just these two for some reason.
Both versions in the screenshot are on Qobuz (note the Qobuz icon), so this is why you cannot download the release. Likewise, Qobuz releases can also be included in your library, which is why they share the library icon.
You will need to check your library when you return home. Meanwhile, you could try restarting ARC.