Attention Trainers! We are currently aware of an issue that prevents users from downloading update data on the Switch version of #PokemonUNITE. We apologize for the inconvenience, and are investigating a solution. Thank you for your patience!
This issue is still being investigated. If you are continuing to experience this issue, please try redownloading #PokemonUNITE. We apologize for the inconvenience once more, and thank you for your patience!
Source: Official Pokémon UNITE website