Error message, then success messsage

Hi, I’ve got a form using both Mail 1 and Mail 2. When the form is submitted, it shows 2 ‘loading’ revolving arrow icons, then shows the ‘There was an error trying to send your message. Please try again later.’ error message, then quickly shows the ‘Thank you for your message. It has been sent.’ Both messages do get sent successfully. Any ideas what could be wrong?