Please test and and mark stable media-gfx/gscan2pdf-2.12.2 for amd64 and x86. Current stable 2.9.1 is not compatible with the only available media-libs/tiff.
Thanks for testing, fixing the test failure needs an upstream fix. Let's give it a little while to see if a new release lands. If not backporting the fix by then may as well be to 2.12.3.