This is one a Mikrotik CCR DHCP server, but I've never seen this. I have a client, I think an Apple router MAC 20:C9:D0:11:56:F0, that the DHCP says "declines IP address x.x.x.x" several times a second.
I have it on static assignment. If I take it off static assignment, it just starts cycling through all available IP addresses in the DHCP pool. Which is horrible, so I'm glad it's on static assignment. If I cut off Ethernet to it, it stops for a while, then starts back up eventually. Not sure what to do other than send someone over there to update the router, or secretly brick it and tell the customer to get a new one, lol!
