Not sure how much it helps, but it is No.10 on this list
What isn't clear from the message or that lis is which is the source and which the destination.
As john suggested, before all the edits so I haven't seen the full address, it looks from your replies to him that is the visible-from-outside address of your router. Which makes the message useless for finding out anything, in particular where it is coming from.
It's almost as though it is trying to talk to itself and telling itself it can't.
Is there a separate firewall log in the router? If so, see what that has to say.
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