This might possibly be the beginning of overwork. While its true that Black Clover also had some unfinished panels, that was mostly beta and some inking. Heroaca has whole pages which were just sketches that might not have even been inked in. It might literally have been pencil with some screen tone added in. Horikoshi has lately been under a huge amount of work; supervising the anime in general, meeting with anime staff, coming up with original stories for both the jump festa OVA and Vol 14 OVA, which are both probably 50 page drafts like the Jump festa one was, redrawing pages for volume releases to correct some things and phrases, colour pages all of which are done on top of the weekly chapters and planning the story. While its true that he probably is putting more input than needed into the anime work as staff themselves are competent, I have a feeling he's like Oda, if he's been asked to provide ideas for something he'll go all out.