While I have never experienced this before with any of my apps, I do remember one case where a customer had a form submission email configured that was identical to an email configured within another one of their apps, and so it seemed as though they were receiving duplicate emails because of that.
Our support team would be able to investigate this for you and see what may have caused this with our internal tooling. That way, we could ensure you and the users of your app do not receive duplicates in the future.
If you decide to reach out to our support team, here are some helpful pieces of information to share:
Form submission email in question
Date/Time (including your timezone) of each email received
Screenshot of the email that shows the subject and the body
Please let me know if you have any questions about what I’ve shared here.
I have an online session with Carl in a couple of hours, just to look over what I have done so far, so it may be a case that he spots the error. If not, then I will contact support.