You refreshed your Salesforce Sandbox and Heroku Connect prompted you to recreate the connection to the Sandbox organization. After you exported your configuration and deprovisioned the connection, your mappings disappeared. What happened to them?
The configuration of your mappings and connection is stored in the exported configuration you created. When you deprovisioned the old connection, Heroku Connect cleared the schema so it could be reused. When you import your connection, we will re-synchronize the data for your mappings.