@Pixichi
Well it could be a number of reasons for quality
A)the artist is pushing a lot of content at a higher rate meaning "lower" quality work
B) The artist is bad at drawing certain scenes
C)Or they have an assistant who is in charge of areas that the artist lacks in, who draws in a different style but is trying to be consistent
C)I mean the last couple of chapters has been a lot of mob characters they have to draw out and no one wants to draw some guys face who's unimportant to the plot