Printers accept things (anything) on port 515(LPR),9100(RAW), FTP(21)
If they are print ready, they will print them, and they can also be used to install firmware. It sounds like you have one of 2 things happening.
1. There is a virus sending garbage data onto the network, the printers are receiving that data and failing to interpret them, causing a reboot/bootloop.
2. Someone is running a script or program to update printers on the LAN, and the update file is corrupt, or incorrect for the printer on which it is being applied
Of course there may be others, but these seem likely.
Everything is going to be guessing until you run a wirshark trace and extract the data from it that is faulting the devices.