someone could be charging their smartphone or device on a computer. could be a printer or a lot of other things that might be connected to a computer.
Try to narrow it down to a computer. turn off one computer at a time until you identify the computer.
My office is a small LAN with 20 users. Recently an unknown entity appeared on the LAN and uses an IP address of a known computer, but with a different MAC. It seems that entity is hosted on another computer, but my antivirus can not identify it. We know that the entity is hosted in a computer because we turn off all computers and the entity also off, but reappears with no identifiable pattern.
I need help!