See which ones are hitting your static IP and verify that this is not on a print server bit banging your printer with print jobs.
I could have dug into this more, used Wireshark, etc, but why? These printers are not that expensive and my time is extremely valuable.
The theory I've seen that I think holds the most potential is these printers having sensitivities to something in the network environment - number of broadcasts, etc. The issue happened on two different print servers. The problem did go away after I rebooted servers, however, which includes 2008 R. The problem springs up on both of them at the same time when it does happen. The two Zebra GX420d's worked fine when connected directly to a laptop or on a small network with a switch and a laptop, so the hardware isn't failing. We also tried all the basics - firmware, drivers, cabling, IP conflicts, etc. Has anyone else had the same issue that was resolved or could anyone maybe think of something we are missing? We have tried everything suggested in the above thread and the steps taken in the original query but nothing makes any difference whatsoever. This thread describes the exact same issue we are having. They have been functioning perfectly until now and nothing has changed on our network that would cause this to happen. We have over a dozen Zebra GK420d label printers that constantly fall off our network for no apparent reason.
If your network is small look for a malfunctioning pc or server that is sending out a lot of broadcasts. We solved the problem by putting the printers on a VLAN to separate them from the main network. We found that the printers are very sensitive to broadcast traffic. We have had this problem with the Zebra GK420t printers.