Players are currently reporting that Pokemon Go is encountering an issue with Spotlight Hour that effects a Pokemon's ability to obtain its Hoenn Celebration event move during the 1/19/2021 Shroomish Spotlight Hour.
Update: We are also seeing reports that neither Rayquaza or Metagross learn their event moves (Hurricane and Meteor Mash respectively) during Spotlight Hour.— PokeMiners (@poke_miners) January 19, 2021
It appears the server has also been reverted to a previous pre-event state as well. https://t.co/DZ1NVlA07b
While some players are currently saying that the issue has been fixed and will not effect Spotlight Hours that are celebrated somewhere globally every hour moving forward, it is the recommendation of the Gamepress staff that all players should wait until tomorrow (1/20/21) to evolve their Metang into Metagross for Meteor Mash or claim their Hurricane Rayquaza. By this point we should be 100% safe, as we currently have no guarantee that Niantic will fix this error in Pokemon that lack their special moves due to being evolved/caught during the issue.