Pokémon GO developer Niantic has confirmed that login issues are affecting a number of players in Japan. The reason behind these widespread issues have yet to be known, but Niantic has updated an official Japanese support page that informs users about some of the potential problems, such as forgetting passwords, signing in to accounts properly, etc. You can visit that particular page by clicking here.
Source: Pokémon GO Japan @PokemonGOAppJP
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