This may be completely unrelated, but for the record:
I’ve got the same printer (Brother MFCL3750CDW), which used to work quite well on Fedora, using the drivers, that can be downloaded from the manufacturers site. But recently, it stopped to work, all of a sudden. From that point on, the printer queue acted basically like a black hole, accepting all documents, but nothing was received by the printer.
I tried different port definitions (ipp, lpd, socket) without success. In the end, I changed the LogLevel to debug in /etc/cups/cupsd.conf, and studied the log messages with “journalctl -u cups -e -l”. As it turned out, the printer driver was missing a certain Perl module (File::Copy). Well, that was something, that I could help with.
Long story short: simple
dnf -y install perl-File-Copy
fixed my problems.