Originally, the anomaly was found by BedBreaker43 (Andrew Regen) after he explored an empty town on a server (most likely ghost of it) which after exploring surroundings enters the buildings and gets trapped into something resembling the overworld which is closed in itself, later he escapes the anomaly.
After that the anomaly was reported 4 years later by someone named KassandraRossenberg666 on minecraft creepypasta wiki, as the authour said "I walked, walked, had already passed about a kilometer, nothing" also the author mentions someone named "ArgatN2" and "ArgatN1" and that he "realized that it was a simulation" it is currently unknown what the writer is talking about and he might have overexaggerated some parts of his story since we have no proof of anything that he wrote expect screenshots which closely resemble the things that we can see in the video made by Andrew