Here is the response I got
If you are using 2.9.9.1, then the issue is not with the plugin.
The most common reason that admin notification emails are not sent/received (aside from the issue in 2.9.9) is the host. I have an article on my personal blog that discusses several of the possible issues: https://www.butlerblog.com/2013/09/24/troubleshooting-the-wp_mail-function/ Another possible issue that isn’t addressed in that is that many hosts, especially with shared hosting, throttle the sending of messages. So because the admin notification email comes immediately after the user email, some hosts will throttle that email.
The best way to avoid any of these issues is to configure your setup to have wp_mail send through SMTP. This gets your email process away from any possible issues and/or rules that your host may institute regarding script based email. There are some links in the article I referenced above and I have another post about that here: https://www.butlerblog.com/2013/12/12/easy-smtp-email-settings-for-wordpress/
Unfortunately, that doesn’t help my issue because I have already had SMTP mail set up and everything email related on the site is working properly just not the admin notification. But maybe this’ll help you.