If you are missing a project, please ensure that you are logging in with the same credentials that you originally used to create the project. For example, if you logged in originally with Google, you will need to use Google (with the same email address) to see your projects. If you use a different email, or a different method such as Facebook or an Adobe ID, you will be logged into a new account with different or no projects.
Please also be sure to check Spark's status under "Creative Cloud" here: https://status.adobe.com/. If there is currently an outage, your project may reappear shortly after the outage is resolved.