I'm not surprised that someone has translated more chapters from the 3rd volume. The whole volume has been available for a few weeks now(and available on the net), not to mention the magazine releases. I assume the chapter that was uploaded briefly was apart of a commission or some group wants to offer exclusive access to their paid supporters first.
The remaining chapters in the volume are mostly about establishing the world 'RPG' mechanics and how the MC is different from other people, this is mostly conveyed through the MC experimenting in the labyrinth. There a little more loving with Roxanne too, but seems like we will have to wait for volume 4 for some real further progress in the story.
The pace of the manga is quite slow and I wouldn't recommend getting into it just yet for someone who hates the waiting, but the story is pretty good and detailed. Also I really like the eroticism in this, its far better than the usual juvenile stuff nor does it come across as crass or forced fan service. I was quite surprised how good the eroticism is, because at first the manga and MC seemed fairly creepy with the whole slavery thing, but luckily it doesn't seem to get too far into that king of fetishism. Although I would be happier if it wouldn't use slavery for establishing relationships at all. Roxanne is really cute and I wish to see her side of things more. Those floppy dog ears are cute af.