Emails get sent, But No Success Message!

[davecollado]

When I enter all the required fields the email is sent, but the form just sits there. No success message. No spinning arrows, and no redirect to thanks you page. Once I uninstall Contact-form-newsletter, everything returns to normal and works fine again. Also, even stranger, with the plugin installed, if I leave out some of the required fields, I do get the error messages. It's only the success message and the Additional setting on_sent_ok that are not working. Please advice