Tinkercad has several ways to sign in. When signing in, it is best to consistently use the same method, as to not generate a new account.
A common scenario we have seen is users creating new, empty accounts after signing in with a different sign in option.
For example , if you have been signing in with Autodesk credentials (email or username), then clicked "Sign in with Google" or another social sign in option, then you will create a new, empty account."
To sign in with your Autodesk credentials, click "Sign in with Email" then use your email or username to log in.
The good news: Your data is all still there.