If the naming conventions are the same in the Ubuntu libraries as they are in the Mac libraries (no guarantee there, but I was just looking at them, and they look almost identical), it's not finding the appropriate driver for the scanner. I know that the SnapScan 1212u will work with Ubuntu, because I came across several discussions, as I was looking for a solution for my Mac. Have you installed the Linux SANE libraries? Agfa scanners were very popular for years, and mine still works great, too. I know that numerous Agfa scanners, including the 1212u are supported in the SANE backend libraries for Mac, allowing TWAIN acquisitions with devices that may no longer be supported with current scanning software.
I think you just need to install the SANE libraries, backends, and any interface (it's 5 files on the Mac). There's some additional troubleshooting information and links to files, here.