STP - Thank you.
Their isn't any options to access STP settings, I can find. I do have 3 un-managed switches (none of them daisy chained). The only other thing I have that is unusual is I am running ethernet over cable (MoCA) to get a hard signal to the back of my house.
I have the exact same issue - new RT-AC87, once an hour about a 1/2 dozen of these messages. I have no QoS, etc. I have tried various things to fix this: Move to CTF Level 1 switch control, assign all LAN devices static IPs, nothing works.
On a related note: I had a RT-AC66U I was using...