scanning with a samsung 4600 in ubuntu

My trusty old Samsung SCX-4600 scanner/printer refused to be recognized anymore by my laptop running Ubuntu 18.04. Trying to initiate a scan failed both from SimpleScan, XSane and the command line:
$ scanimage -L             

No scanners were identified. If you were expecting something different,
check that the scanner is plugged in, turned on and detected by the
sane-find-scanner tool (if appropriate). Please read the documentation
which came with this software (README, FAQ, manpages).
A longish google quest led me to a suggestion that fixed it for me. The mysterious SANE_USB_WORKAROUND setting resolved the issue. The scanner is recognized again:
$ scanimage -L
device `xerox_mfp:libusb:002:004' is a Samsung Samsung SCX-4600 Series multi-function peripheral
And scanning works like a charm:
$ scanimage --format=png > /tmp/some_document.png