Chapter numbers here are also different from pixiv starting from chapter 20 (the summer festival arc); 27 here is a January bonus on pixiv, 28 here is 20 there, and the 8-chapter lead is maintained to this day.
Basically the summer festival arc doesn't exist on pixiv at all. This also explains why the story went from July to January from one chapter to the next. I'm worried for the canon in that case...
Translators might want to find a good approach for this. (Maybe asking Izumi-sensei directly?)
I mentioned this in an earlier forum post, but to sum it up, the order of chapters on Pixiv, in the manga, and on Twitter are all different. During the manga release, we followed the manga order as it was the most curated version. The festival arc appears only in the manga and Twitter releases, with the Twitter version partially colored by her.
As for our approach, occasionally I may rearrange a chapter to a better position, as I did with the Kotatsu chapter. However, I usually refrain from doing so because once Izumi has completed enough chapters, she will refine them and release Volume 2 of the manga, which I will then use as the more canonical ordering. And when that happens, I might even have to update a few chapters because she's known to sometimes change dialogue from the web version to the manga version.