I got a Samsung SCX-4521F. I got that working about a year ago using the Samsung unified driver. I haven't used the scanner in quite a while - several releases have rolled by... So, today I tried to use it again and it didn't work. It seems, that somewhere during that time the configuration got lost?! I wouldn't rule out an unintended deinstall (don't drink & (re-)(de-)install!)...
Anyway, I downloaded the SUD from https://aur.archlinux.org/packages/samsung-unified-driver/ and used the install-scanner.sh script to install Scanner support (printer is working).
Plugging the MFP in USB => messages.log:
Jul 5 21:19:12 mars kernel: usb 3-7: new full-speed USB device number 6 using xhci_hcd
Jul 5 21:19:12 mars kernel: usblp 3-7:1.1: usblp1: USB Bidirectional printer dev 6 if 1 alt 0 proto 2 vid 0x04E8 pid 0x3419
Jul 5 21:19:12 mars systemd: Reached target Printer.
Jul 5 21:19:12 mars systemd: Started Configure Plugged-In Printer.
Jul 5 21:19:18 mars kernel: usblp1: removed
Jul 5 21:19:18 mars kernel: usblp 3-7:1.1: usblp1: USB Bidirectional printer dev 6 if 1 alt 0 proto 2 vid 0x04E8 pid 0x3419
Jul 5 21:19:18 mars udev-configure-printer: Re-enabled printer ipp://localhost/printers/Samsung-SCX-4x21-Series
Starting "sudo xsane" (it used to work without being su before, but right now I would be glad to scan as root):
Don't know where that ORION-thing comes from, but neither of the two are working. I select one of the two, and when trying to scan get an error messages "Couldn't start Scanner".