Okay. I just finished reading the thread discussion, which I completely skipped before reading for fear of spoilers. This is why I ended up reading the earlier drafts for the prologue and first chapter, not realizing the latest PDF in the thread revised them. I'd ask the jannies to edit the OP to clarify this for prospective readers.
I also see now where a lot of my confusion with the text came from. The reader is more or less expected to be familiar with species and character lore from previously published drawings predating this story. It wasn't a confusion fatal to understanding of the plot-- there're enough context clues to "catch up" with most of this, save for things like visual descriptions-- but it does make it just that much harder to get into. Given how talented an artist you are, Rev, you don't really need to alter the text all that much to solve this-- unless you want to, I suppose. I'd use that strength to my advantage if I had it. Referring back to that other thread: either a supplemental reference "codex" book (a compilation of these aforementioned drawings), or embedding the images within the text would work. I'd toy with the exact execution but that's how I'd go about it. I think it's the single greatest issue with your story so far. Just, when proofreading, try to pretend for a second that you're a reader going in blind, without any prior knowledge of anything in this universe.
An idea I had-- if you don't want to go the separate codex route-- is prepending each chapter with a "species/figures you will encounter..." page or section so that each chapter reveals only what it needs about the universe progressively. If a particular entry would spoil the chapter, then I'd fall back on textual descriptions/introductions, which you can then maybe follow up with an illustration on the following verso (left-hand) page once the reader seeing it wouldn't ruin anything. You may be hesitant to simply "loredump" with a separate reference book, but consider that you're already effectively doing that via the soft requirement that readers be familiarized with preexisting lore & characterizations outside the text. This would simply compile it conveniently for new readers. There's also nothing inherently wrong with this, especially given the relatively dense lore which would be difficult to introduce gradually or without affecting the pacing, as you noted. Correct me if I'm wrong-- since I've yet to get around to reading the actual books-- but Tolkien did something similar for the Lord of the Rings with The Silmarillion.
Again, I believe this is actually the most glaring issue with this work. Beyond that, the dozen other things others have mentioned can possibly use fine tuning, sure, but its solid work thus far.
Good job, Rev!