For that feature, the transactions need to be made while being logged into the site (so the plugin can recognize a user and store the transaction data for that user). Are you testing with an account where the transaction was made after the user logged into the site?
If you are just allowing anonymous checkout (guest checkout), then the plugin won’t have any idea in terms which user is purchasing what.
Enable the debug logging option in both the Stripe plugin and the emember plugin. Then do a test transaction with a user account that you created (for testing). Does that transaction show correctly?