i got to agree with wolfman, without being able to see the system, i would recommend downloading all the 'brother' drivers. If the additional drivers settings have no propreitary drivers listed then that means either the 'brother' drivers are not installed, or the "brother" drivers are not proprietary. Occasionally, when booting, the drivers may fail to load and will only need a reboot.
if they are not proprietary, then they can be changed by any developers(and this may have happened) and you may need to reload the original drivers from the manufacturer.
Try not to get upset if things have been changed by the developers, especially with a beta version, and especially with a minimized beta version like UbuntuMATE. In order to keep an OS small they will get rid of anything that may not be in use anymore and won't put proprietary software, so it is possible that your drivers are no longer included. It does leave us looking for our own solutions. I'm not sure how popular Brother products are, but if you have a printer that is rare or old, or even worse one of a kind and old, then you'll probably have to find your own drivers anytime you do a clean reinstall. Shouldn't be a problem with the upgrades, but you might want to keep a copy of the drivers, just in case.