Had the same issue with Ubuntu 18.04 and Samsung SCX-3205W. Over Wi-Fi the printer worked, the scanner did not. In Ubuntu 16.04 both printer and scanner work.
Used advice from https://askubuntu.com/a/979180/125250 to fix the issue by adding `ATTRS{idProduct}=="3200", ENV{libsane_matched}="yes"` line to `59-smfp_samsung.rules`.
Had the same issue with Ubuntu 18.04 and Samsung SCX-3205W. Over Wi-Fi the printer worked, the scanner did not. In Ubuntu 16.04 both printer and scanner work.
Used advice from https:/ /askubuntu. com/a/979180/ 125250 to fix the issue by adding `ATTRS{ idProduct} =="3200" , ENV{libsane_ matched} ="yes"` line to `59-smfp_ samsung. rules`.