A common issue with most ink jet cartridges, mostly with Brother cartridges, is that the cartridge feels like it doesn’t want to snap into place. This issue may be caused from the plastic covering the ink hole, the plastic film over the hole where the ink comes out. Some times the plastic film over the ink hole is thicker than normal and when trying to press it into the printer the plastic won’t pierce like it normally would.
Next time your cartridge is not snapping into place, remove the cartridge and look to see if there is plastic covering the ink hole. Try breaking the plastic yourself with a pen or needle, and then reinsert it. Don’t worry about ink leaking out. Cartridges have mechanisms within them to prevent ink from leaking out unless inside of a printer.