I've been trying to find a web-original short story I read a couple years back.
I found it on Imgur, text on an image, fairly long, it may have been a 4chan greenpost.
The essential premise was a reminiscence from the point of view of aliens encountering humanity. Everything goes really well but something is subtly wrong.
Then the protagonist alien encounters a human child, and perceives something monstrous and shadowy "behind" them. It turns out that humanity has eldritch horrors looking out for them and they don't tolerate the aliens' interference.
Humanity has no idea why the aliens packed up and ran away overnight.
I thought I read it in a compilation of "Humanity F*ck Yeah" stories, but haven't been able to find it again.