Could you please confirm that the "To:" field in the Email Receipts settings is configured with an Email field?
Yes it is.
Thanks. Could you please email the form ID to email@example.com? To find the ID, open the form then copy the last part of the URL shown in the browser's address bar - the content after "#d=" in the example shown below:
If possible, please include in your email an example email address that did not receive a receipt.