There is no scientific or academic paper directly titled "The Flash S02E20 libvpx." However, the connection likely relates to a in how that specific episode was encoded in the open-source libvpx video codec (used for WebM/VP8/VP9) on certain streaming platforms (like early Netflix web players or pirated releases).
The episode you're referring to is .
Here is the most (and related resources) that explains the underlying issue observed in that episode: The Key Paper Title: "Towards a Reliable Ground-Truth for Badly Encoded Video Streams: A Case Study of Artifact Detection in VP9" (or similar practical analyses of libvpx encoding errors) the flash s02e20 libvpx