I think there is a bug in the update. When I updated the game and tried to sign in it said "There is no Pokemon Go account associated with this email". I don't know if this has just happened to me but I would advise you to not update the game. I'm going to make a list of people who are being affected by this bug. (Reply to this thread so that I may add you to the list.)
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The following user groaned Python for this awful post: