This is a weird one and it's happened twice in the past couple of months. We have port security active on our switches and twice we've seen it get tripped by an invalid MAC address like e8be.5bd3.5558. It's as if the machines that are connected to it temporarily switch to a different MAC address, which I've never heard of.
If I recall correctly, the first time it happened was with a printer, but I'm not 100% sure. Last night it happened again with a workstation. I did find someone else on a different forum who had experienced it but they did not know the cause.