I upgraded to 17.10 last month or so and since then scanning with gscan2pdf has not worked.
It did work under 17.04 and 16.04 though. Funny thing is, my scanner appears under scanimage -L and actually scans using scanimage > /tmp/test.png. gscan2pdf, however, gives me "Error retrieving scanner options: error getting option 6: Invalid argument". I tried under xsane and that's giving me the same problem.