Let's back out a bit and look at a larger picture:
The series started at the beginning of February. By the time Volume 1 was released at the beginning of June (which is the 200ish pages of chapters 1 to 5), the author had put out a chapter each week for 17 weeks (4 months). And even for his week "off" for the volume release he still had to prepare the omake pages.
From chapter 18 to 25 is about 3 months, and we had 8 chapters out of a maximum of 12. Volume 2 has just released covering chapters 6 to 14, another 200ish pages.
It seems rough to think about "losing" 4 chapters in 2 months; but if you were to alter it in your mind that each of those off weeks really should have come after each 8 chapters we'd be in the same place we are now.
And you can also see right now on Bookwalker that Volume 3 is planned to be due not in another 3 months in December, but in just one more month at the beginning of October (though they do append "Date subject to change," which could just be standard). Doing quick & dirty math, another 200 pages would be chapters 15 to 24.