Some Trainers might experience an issue where it appears that gameplay progress has been reset. Please be assured that your gameplay progress has NOT been lost. It remains safe and intact.
You may have inadvertently created another Pokémon GO account. This happens when you create a Pokémon GO account with one login method and later attempt to sign in with a different login method or email address.
To resolve this issue:
You’ll need to log out of the account you’re currently signed into and sign in with the email address and login method you originally used to create your Pokémon GO account.
In Map View, tap the Main Menu
At the top right, tap Settings
On the Settings screen, scroll down and take note of the linked email address and login methods under the Account section.
You are currently logged into your account using this combination of email address and login method.
Tap Sign Out
Sign in using the same email address AND login method used when you originally created your Pokémon GO account.