Short story collections generally contain stories which all seem to have "taken place in the same world" or "been filmed with the same camera." In other words, the stories in collections are often stylistically cohesive, which is to say, all pretty similar. It seems like this is thought to be a necessary component of The Short Story Collection. I've always been kind of under that impression.
Leidner's disregard for this formula is, I think, one of the things that makes Under the Sea so delightful and unusual. In terms of genre, style, attitude, approach, etc. - the stories are all over the place. They're sometimes realistic, sometimes fantastical, sometimes silly, often funny, sometimes serious, sometimes sad. Finishing a story, you're never sure what type of story is coming next. It's fun and refreshing. (One thing, though, which does pervade: Leidner's humor. I laughed a bunch.)
Another thing that struck me is this: Leidner's way of storytelling seems to break down or subvert "literary pretense/expectation" and often includes, or references, other unexpected "non-literary" storytelling tropes and forms, like popular movies or TV. I don't want to get into too much analysis, or spoil things, but "Avern-Y6", for instance, is told from such detail in the 3rd person that it almost reads like a script or movie (which is complementary to the bizarre content of the story).
As opposed to following standard short story conventions, Leidner often leans into the conventions of other story forms, and pulls it off: it's effective, enjoyable, non-pretentious, and, in literary fiction, atypical.
My favorite stories were "Bad-Asses", "Avern-Y6", and "Lost in Translation"
I really enjoyed Under the Sea. I think you should buy it and read it.