I think they made a mistake and this is really chapter 38. This doesn't feel like a side chapter at all. There is actually what seems like a major revelation in this chapter
Spoiler:
Yami was wounded very badly in the past and lost her memories of the event. To this day she still hasn't recovered them. It was the only time Mikado saw her in such a bad state. Nobody knows what happened to her back then, but Momo thinks Nemesis knows something.
Yeah, I think it was a printing error on JUMP's end. They'll likely issue an apology in the upcoming SQ19.
Spoiler for revelation:
Since Mea is practically on Team Good Guys now, Momo will likely try to siphon the info from her first but be met with a roadblock instituted by Nemesis. And as we saw in an earlier chapter, Nemesis doesn't supply info without some service, so it'll be up to Rito to 'satisfy' her
Least we know now, that Rito is a normal boy. Must say that the manga is progressing nicely. Its always a good read and the quality is great and is worth the long waiting time