This happens in more than one facility. 4 Lexmark and 1 Dell printers are changing port speed from 1Gbps to 100Mbps and even to 10Mpbs for reasons I can not explain and multiple Dell and Lexmark printers that are not. The firmware on each of the printers have been updated to the latest release as well the switches have been updated to the latest beta firmware. This happens randomly throughout the day and I am not sure if this is a printer or switch issue. I have done some research on the printers with not luck and am not sure if this is a switch issue. Thanks for any assistance that can be provided.
Are you sure the devices have Gigabit ports? Most printers, including big multi functions don't. Some of the older printers also don't auto sense well and some times require hard coding the port to 100mb full duplex or half duplex.
If your printer truly is 1gb ethernet I'd suggest doing a packet capture and looking for anything that might be causing an issue. You can always call support for help with the packet capture and they look through those things all day long.