Sorry, I missed that.
Our tickets get sent via wp_mail() or WooCommerce’s email code. Therefore, if your tickets are being delivered inconsistently, you might need to install an SMTP plugin: https://wordpress.org/plugins/search.php?q=smtp (none are supported or guaranteed by us)
To be clear, this isn’t an issue specific to our plugin; email deliverability is an issue at the WordPress-level of your site or possibly even at the domain-level or IP address (if associated with SPAM, accurately or not).
Please let us know if you find out what solution worked for you.
Thanks!