A couple of quick thoughts, based on your conversation about this story.
The people of Ib are described with green skin, bulging eyes, etc. Is this an early example of HPL fish/amphibious people motif, like Shadow Over Innsmouth? I agree that this is not one of the Dreamlands stories. I think it's a one-off that HPL did early in his career that touched on several things that he went back to in greater detail.
It also sounds like Brandon thinks the truth is out there, recorded on these cylinders and papyri. I recently did a re-watch of the X-Files as well.
I found the story here: