It isn't October 12th yet and we do have the first polemic
Pablo Iglesias, the leader of Podemos, has declined the invitation to the King's reception at the Royal Palace after the parade. He says that his presence "is more necessary defending social justice that in this kind of events" or something along the lines. He added that some journalist told him that the event was "a bit of a boredom". Earlier this week his party was also news because they claimed to not have received the invitation, just to realize later (after the Royal House said the exact day and hour they sent it) that the invitation was send to an e-mail account they had not checked
Oh well, I have the feeling that some absences will be more a relief than an offense for the RF, anyway