Hello,
please consider to add the following udev rule for Brother scanners:
# Brother
ATTR{idVendor}=="04f9", ENV{libsane_matched}="yes"
Source:
http://support.brother.com/g/s/id/linux/en/instruction_scn1c.html?c=us_ot&lang=en&redirect=on
This works well for me on Fedora 27.
Thanks!
Regards,
Thomas