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)
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 .