It is observed such on rb411 in different places on v5.2 all well
07:23:37 interface,info ether1 link down
07:23:39 interface,info ether1 link up (speed 100M, full duplex)
07:26:27 interface,info ether1 link down
07:26:29 interface,info ether1 link up (speed 100M, full duplex)
08:04:27 interface,info ether1 link down
08:04:28 interface,info ether1 link up (speed 100M, full duplex)
08:04:35 interface,info ether1 link down
08:04:37 interface,info ether1 link up (speed 100M, full duplex)
08:07:32 interface,info ether1 link down
08:07:34 interface,info ether1 link up (speed 100M, full duplex)
08:09:12 interface,info ether1 link down
08:09:14 interface,info ether1 link up (speed 100M, full duplex)
08:12:09 interface,info ether1 link down
08:12:11 interface,info ether1 link up (speed 100M, full duplex)
08:28:57 interface,info ether1 link down
08:28:58 interface,info ether1 link up (speed 100M, full duplex)