I have done an exhaustive search on google and your asus forum posts for an explanation of this syslog entry (forgive me if I accidentally overlooked my answers).
There where quite a few posts about this in merlin's subforum and the RT-GT5300 thread, yet I feel I've either missed the answer...
I have noticed that a lot of the routers have gotten a firmware update lately but it does not seem to be the case for AC86U. Any one here know if it will get an update any time soon?