Brother printers have went this way too. Mine incessantly complains about low toner even when I use brand new ones because they aren't brother branded.
2. Speaking from experience doing support for a lot of them, brother* printers are notorious for not realizing the toner (even with originals) was changed. There are ways to reset the counter though(Holding two buttons while powering on). It's usually mentioned in the manual.
* It's the only brand I know with that problem.
I was thinking maybe I moved the printer and it is not level?
Unlike the inkjet where it shines a little LED through the cartridge (covering with black electrical tape makes it think it's always full), laser toner I think has an id chip on the cartridge and the printer just maintains an internal counter as to guess when it'll run out. Reset that, and make sure the option is turned off that stops it continuing to print once low (networked models have a webpage you can go to to turn these from stop to just warn).