Hi,
Searched this and found several old threads but i cant figure out a solution.
Started to get this yesterday. Ive switched to a brand new router, configured it all manual (no export/import to avoid MAC duplicates) and now this router behave the same. What can i do?
Are you using RSTP, intentionally or not?
Dont know 
RSTP is checked on the bridge. Guess its default since i have not touched any of this.
In our network, we are using RSTP for loop protection. If there is a momentary interruption, RSTP will flood packets out all ports while it figures out the new pathway, and we will see that message occassionally. If you aren’t using it for loop protection, you may actually have a loop somewhere and RSTP is doing it’s job. If I remember correctly, the message tells you which port it was seen on. You can use that as a clue to follow back to the culprit.
Cheers
Only using 2 ports on router. Ether 1 is for WAN and ether2 is connected to a 24 port switch. No equipment added, this message has just started to pop, dunno for how long.
I get DHCP offer IP address constantly to the MAC address for ether2. “dhcp offering lease 172.32.101.98 for C4:AD:34:A1:4D:9D without success”.
Must be a loop in the 24 port switch somewhere. Have you checked all equipment attached to this switch?
No i will disconnect one at a time and see… what equipment could it be ?
I have had issues with equipment that are connected and redundant for example via LACP and the equipment then builds and internal software switch which links the two sides together and creates a loop. Should not that when this has happen it is 100% my own fault for missconfiguration!
Testing one by one is a good start.
Please be aware that this issue can also occur when you have an IP conflict on your network. Observe your arp tables, or just check by hand and make sure you have no IP conflicts.