Error : flapping between port sw_matm-4-macflap_notif

[punnawit]

Regarding that error, I'm not sure what caused it.
Initially, I checked the port status and could not find the loop.
What should I do? The details of the diagram are as shown in the figure.

[balaji.bandi]

we do see that logs when the wireless client roaming,

[Flavio Miranda]

Can you provide the following command:

show run int g 1/0/15 and 1/0/20 ?

show log could also be nice.

[Leo Laohoo]

Trace down that MAC address and you will find someone has "bridged" the two ports with a hub or a machine with 2 NICs.