There are two different chapter 5's in the raws, it's the author that fucked up the numbering
You would think with split chapters being so common nowadays someone would not be so confidently wrong about something like this. The 4th page of kitsunedawn's Ch 5 (the first non-ad page) says "Episode:5前編", so it was very clearly intended to be a two-parter.
Checking the official raw the two parts were each split further for at total of seven parts (5.1.1, 5.1.2, 5.1.3, 5.1.4, 5.2.1, 5.2.2, 5.2.3). Chapter 16 is also a two-parter, with each part also being split.