Looks like the Grimm creators might have known that their days were numbered as early as April 2016. I think there were rumours that the show might end up getting cancelled if it didn't perform well ratings wise, so the creators had to come up with the season 6 plot with that idea in mind:
Quote:‘Grimm’: NBC Keeps Options Open With Shorter Season 6 Order
That is not a fixed number, as I hear the pickup is for a minimum of 13 episodes, with a likelihood for more.
http://deadline.com/2016/04/grimm-season...201742272/