Often times WooCommerce Subscriptions will fail to renew for a recurring Subscription because Cron is either not working correctly on a site or because of this. For traffic based firing of Cron, I suggest using JetPack Monitor. It solves this limitation easily and effectively.
For troubleshooting when WooCommerce Subscriptions Not Renewing (or other Cron based scheduled events) I like to use WP Crontrol. It’s great for getting a better idea of what’s happening with your site’s Cron jobs and most times the plugin will print an error on the WP Crontrol configuration page that will give you the right direction to head in for troubleshooting. Often times you will need to work with your hosting provider to resolve the issue. If you are running your own server, then this will be the same error that shows up in system logs.