a warning. I would wonder how you set up those printers and how your router/dhcp server is set up. Personally, I like to go with static addresses for printers and have set them up in a school. I put a label with the IP address on the printer as a troubleshooting aid. But, to do this, you need to properly set up your router/dhcp server so that a range of addresses is available for static use. For instance, I might begin the dhcp range at 101 which gives me 100 available static address and 150+ for dhcp. This prevents IP address conflicts if that's what your getting. This would occur if you had a static address set up on the printer but turned it off and your dhcp server saw the address as available and gave it to another device. What would happen when you turned on your printer is that it wouldn't work unless you gave it another IP address. Does this make sense? Good luck.
I work at a school and we ordered 30 of the Brother HL-5370DW printers. They randomly drop the IP address and we have to set them back up as if they had just come out of the box. We called Brother and they just said that is was our network's fault. They were of NO help whatsoever. We checked our network and found nothing that would cause this to happen. We called them back with these findings and they still refused to work with us. They would not help us because we were technically out of warranty, but our original call was when we were in warranty. Their customer service is atrocious at best. I will never buy another Brother product again.