Based on the comments from a lot of these chapters, it seems to be that, when published in the magazines, 9 pages isn't all that unheard of for the chapters. If you compare it to the average from the volumes, it's important to note that the Volumes consolidate chapters sometimes, which is why the magazine chapter count is higher than the volume chapter count.
For reference, this chapter will likely shift back about 6-7 chapter numbers when published in Volume 18, whenever that will happen, which will probably be either later this year or sometime next year. Take note of the last 7 chapters of Volume 17 versus the 7 chapters after it, and you'll see they repeat because of this discrepancy. This will resolve once Volume 18 is out and its pages are used to fill out these chapter entries instead. It will also mean these comments made for the magazine-published chapters are going to be connected to the wrong volume chapters as of then.
It's also important to remember that mangaka struggle with health issues, likely because of deadlines and workload and such compounding. The manga and anime industry is pretty rough on the creators. Umino has actually talked about her health at times, I feel, in the extras added to the volumes. I wouldn't blame her for slowing down or easing back to some extent, even if that was what was happening.