forgot password function was not working

You have a stylesheet from something else (presumably another plugin) – frontend-forms.css – that sets a text input field with the class “password” to display:none. So that stylesheet is causing the email field in the password reset to not display. So a required field for the password reset is not being filled out when you submit the form.

You can override this in the WP Customizer by adding the following custom CSS:

#wpmem_login input[type=text] {
    display: initial;
}