Not to worry – your account has not been reset – you have just been logged out! If your account has been previously backed up you can simply log in again! See below for the step-by-step:
To restore your progress go to Options > Account > Import Account Progress > Email, Apple ID, or Facebook
If you cannot see this option:
On iOS: Uninstall and reinstall TT2 and follow the steps above
On Android: Clear your TT2 app data and cache and follow the steps above
If you did not back up your account, or if you are unsure, please see Lost Account for the various recovery methods and get in touch with Support -- we will do everything possible to find your account for you!