Damn, who are those people ... but I get it. Authors have months to prepare the 1st few chapters of their series, once you get a weekly serialization, you gotta cut corners to make the deadlines! As for as I remember, except for season breaks, the author hasn't really done a hiatus and that's impressive
I'm an artist and from my point of view, the drastic drop like this happens only with people who simply aren't good enough in their craft and overuse props like 3d models and dolls.
(And to be fair, the earlier art looks more polished, but it still isn't all that good, all thing consider).
Counter to expectations, 3d props are easy to use, but take a lot of time to set up, especially the dolls, so they look semi good and kinda realistic. They are great for really though poses, but at the same time are a shortcut that stop artist from developing their skills and "shorthand" for their art.
This artist is mediocre at their craft and it shows the moment they don't have time to spend hours on one panel and need to rush delivery. They simply don't have mental liberally and freehand skill vast enough to make their work look good enough from the sketch.
I don't blame them for accepting the job, the talent is often in numbers and repetitions, so drawing a weekly is the ultimate excersice, I'm just afraid they don't actually have time to learn craft and will either burn out or experience arrest development and will stay at the level they are now.
In short: the art now is the real skill level of this artist, without the shortcuts and cheat codes.

I just reread chapter 1. the artstyle and body proportions were soooo much better.