If SCP has been discussed elsewhere on this forum then all I can do is apologize for a redundant post. So yeah sometimes you just gotta go to SCP Explained.
SCP-3999 doesn't need explanation, it needs deletion. It's not difficult, it's STUPID. This isn't an example of any sort of complex and clever writing, it's the prose equivalent of word salad.
Internally, this isn't the result of a contained SCP, but the only way for the documentation to be almost entirely corruption (to the extent half of it is a corrupted copy of a different SCP's documentation) is for the SCP to be contained and gotten access to it's documentation.
This is actually a great deal like the horrendous editing of The Difference Engine that left a third of the book filled with similar random nonsense.