Can't blame them, really.
There are 2 chapters numbered 34. Here they're listed as 34 and 34.2 but originally there were listed on batoto as 34 and 35. If you check out the content, both of them show "34" on the title page, yet the credits show 34 and 35. I'm guessing the scanlators thought the magazine made a mistake or didn't realize this and so continued with the mismatch until chapter 38 which was listed as 39. Chapter 39 has the credits page showing 39 but batoto still listed it as 40.
So what's actually going on? If you look at chapter 28 and 29 you may notice that each of them is very short. I'm guessing they weren't planned to be that short, those 2 are, non coincidentally the last 2 chapters before the hiatus. It seems the publisher decided to just merge the 2 chapters for the tankoubon release like they should have been and long story short there are 2 chapters 34 and all these confusion....
If we want to be consistent with the tankoubon we should rename 29 to 28.2 and so on. Just in case someone is going to redo the scans....