Ninja Forms works 'sometimes'

Hi
I just noticed that my forms where showing in ‘maintenance’ so I clicked ‘remove maintenance mode’ in settings and they came back. However on testing the emails do not always work.

On my first attempt the email went to the business owner and I got a copy but the submission confirmation was not received.

On my second attempt the business owner did not receive the email but I got a copy and the submission confirmation was received.

Any ideas what could be the problem? I am using the shortcode [gd_ninja_forms form_id=”2″ text=”Contact form” post_contact=”1″ output=”button”] in my tabs settings.