Well, one of the artists seems to have drawn a lot of BL so my guess is that their clash was how to draw the interaction between the boy and his male aides/friends/family.
The author likely felt that the artist was pushing it a bit too far how he represented the males affection towards the kid. He likely imagined it more like friends, bros and family whilst the mangaka's experience likely made it hard for him to draw things without underlining indication of something more than familial love.
I could be wrong considering that there are 2 authors marked as working on this, but I do think that is the most likeliest reason.