Yes, when you downgrade your Ubesuggest account, you’ll lose information on rakings and historical data, it will automatically remove any projects you have created.
When you sign up again using the same email account, your previous information will not show anymore. That means you would need to start from scratch and add your projects again in case you decide to be a pro user or use the free benefits of the tool.
Side note: when a user downgrades the account, it’s possible to use it with the free benefits.
For more information on how to cancel an account, visit the article How to I cancel my suscription?