A few questions:
How long does it take for the default response to come back to the flow? Is it immediate?
Are you sending it to yourself for testing or sending it to actual users?
Is the recipient in your organization?
Is it in production?
Was it working before?
Can you post a screenshot?
I've encountered issues with Adaptive Cards in emails getting an immediate auto response back--this is due to security processes checking links in the email when as it arrives at the destination. It's possible that you can run into the same issue with Options Emails.