For example, there are descriptions of how dungeons work, in particular that they need a Lord to prevent collapse, that seem to be written from an omniscient narrator's perspective. But that claim is clearly contradicted by Thistle finding the tomes in the Island Dungeon. Which at that point seemed to be more 'dormant' than 'collapsed'.

I don't think that part is a contradiction! There's a few dungeons in the process of collapsing that don't have Dungeon Lords so the collapse isn't immediate, Mithrun approaches the dungeon that he became a lord in thinking it was collapsed/inactive only to be pulled by the demon, I imagine Thistle's dungeon was in a similar situation.

Here's two examples of how it's described

"on the verge of collapsing" "since it's still functioning, if barely, it's believed to have a lord somewhere"

"since it hadn't had a lord for a long time, it was believed to be nearly collapsed"

So I don't think they collapse right away as was the case in the Island (that one I'm pretty sure collapsed immediately because it was spilling into the surface and the demon was defeated)

It's hard to call something in dungeon meshi a straight up plot hole cause the contradictions are in the text itself and part of the story, we learn that thing works x way only to later learn it actually works y way only to later learn even more details (I'm talking about ancient magic) so since the mismatched info is plot accurate I can't think of many contractions that don't make sense with just a bit of excuses.

The one that puzzles me the most and that I think was a retcon is what Tansu says in chapter 19 and repeats in chapter 22

He talks as if this was something unique to this dungeon? But resurrection is said to be possible in every man-made dungeon, maybe in chapter 22 he's talking about specifically the immortality curse on the residents of the golden kingdom but idk how he'd know about that? Or maybe there's something more specific to how the souls are attached to bodies in this dungeon idk that one really puzzles me

According to the glossary that spell is active in most man-made dungeons

I have a question about death in dungeons.

You can be ressurected in any manmade dungeon, that's just a default. Thistle made certain people immortal, but that applies only to them and they are not known to anyone but the Laios party, right? So why does Mr Tensu talk about the death ban in our beloved dungeon as if its some great mystery, as if this dungeon was special? Is it because they found runes and hope to learn how to implement ressurection in other places or is it something else I missed?

Thank you <3

Great question! My best guess is that it was a retcon about resurrection not being unique. Either that or Tansu is talking about the immortality spell in all dungeons? He does say that's what the elves are after but maybe it's just a bad guess because he doesn't have all the information about ancient magic.

The Spell of Immortality. Powerful Vedic Magic