How much of the Sun/Moon anime hate is residual anger from Ash's loss in the Kalos League? It's almost been two years since and I can't find any comparisons for the fallout from the loss - transitioning from a well-received anime with a horrible end into a poorly received anime.
The closest I can think of are Mahou Sensei Negima abruptly ending, and the Osamu Kobayashi episode in Gurren-Lagann. But nothing is a 1:1 match.