Scheduled events has a possibility to not run or run late if there is no traffic during the trigger date.

Setting up WPEngine Alternate CRON could help with this issue.

Alternate cron is a service on the server that checks for “due now” crons every minute.

To enable Alternate Cron, simply reach out to WP Engine Support.

More details here: https://wpengine.com/support/wp-cron-wordpress-scheduling/