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I have tested your embedded form on this page https://www.winecellarinnovations.com/design-form and I was able to replicate mentioned issue by clicking on browser back button.
Most likely same issue can be replicated on your other embedded form as well.
I am not sure if this is happening because of the script conflicts on your webpage. You can try to re-embed your form with iFrame code to see if that will resolve the issue. Inside of this guide you can find how to get iFrame code of your form:
If that does not help, then I would suggest you to use our unique submission feature or unique question feature to prevent duplicate submissions.
Hope this will help. Let us know if you need further assistance.