Every movie this summer has been flopping according to studios. Bourne, Ghostbusters, Suicide Squad, Independence Day, The BFG. It isn't just animation, especially considering Kubo flopped despite being the opposite of a "safe" film.
Zootopia still made a billion dollars, Finding Dory still did extremely well, Secret Life of Pets did fantastically, Angry Birds did shockingly well, and Moana will probably go on to make bank.
This has just been a bad summer, you can't really pin point how or why, there's no trend to be gotten from it, it's just been bad. Sometimes it happens. People this year probably got their fill of movies in Spring because that's when all the good shit came out.