Have you activated another plugin recently @hlogramabc? If so, try deactivating the last plugin you activated and try that.
If that doesn't solve the problem. You can always redirect them to a confirmation page indicating that the form was submitted successfully.
To use the redirect just place the code below in the additional settings of the forms settings interface. Just change the destination URL
`on_sent_ok: "location = 'http://example.com/';"
Hope that helps.