Error text - Confirmation email message

Hello!! The forms work well most of the time, but there is a proportion of emails that do not arrive correctly. A specific text has been configured for confirmation emails, but in some cases a standard email arrives with this text: "Thank you for filling out form! Your information has been successfully submitted. We will process its contents and get back to you as soon as possible."
This message is not configured anywhere and we do not understand where it comes from and why it is sent in some cases.
In these cases the email with the details of the form does not reach the defined admin email, but rather the sender with the concept "Web master. You have a new submission"
They can help us??
Thank you so much

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