https://www.polygon.com/pokemon-go/2018/12/13/18139670/pokemon-go-rhyperior-size-fix-update

Niantic’s latest update to Pokémon Go officially added competitive multiplayer trainer battles to the mobile game this week — a very big deal. Another unannounced change fixes a tiny but important aspect of the game: the size of Rhyperior.

Rhyperior was added to Pokémon Go in mid-October, when Niantic and The Pokémon Company introduced fourth-gen Pokémon to the game. Rhyperior requires a Sinnoh Stone to upgrade, and players were greeted by an abnormally small Pokémon in its final form when they finally got their hands on one.