User blog comment:Miskos3/Fairy Tail 511: The Hell of Starvation, Review/@comment-4829046-20161119172920/@comment-7418318-20161119231950

He draw Zero and plenty of Omakes without any slow downs in the main manga. Then he again and again released two chapters in the same week and once, as Misk already said, 8 chapters in less than a month.

Where other mangaka become sick or take breaks, Mashima pushes out extra chapters.

I don't see how someone who can work that fast would be under time pressure despite not having any side-projects going (as far as we know) at the moment.