@Tarage Chapter 23 might have this warning at the start of it too, but this "chapter 22" is there because the chapter listing itself would be warning everyone about a missing chapter otherwise when there isn't actually one missing. This happens a lot on series with the chapters split into multiple releases for whatever reason too (stuff like 13.1 and 13.2 won't register as either of them being chapter 13 for instance).
The system involving missing chapters is generally a good thing, but in this case it was something that needed to be worked around a little bit to achieve the most comfortable result because people would look at the chapter list and there's just a lack of a chapter as far as they can tell. People probably kept seeing that and asking about it instead of coming across the caution page in ch. 23, so someone decided to fill the blank with this page. This maybe got some annoyance out of people that were tracking the series and looking for new chapter releases in the short run, but in the long run it keeps everyone better informed about the "gap."
@Glomoro Mostly informing you that I really don't give a shit what you have to say, but you completely missed my polite hint so now I have to spell it out for you.