While working on an update of Cornforth Images, ran into an issue where the site was repeatedly hitting the memory ceiling even though the memory has been set to 512M. This occurred with WooCommerce 3.2.6 and WordPress 4.9.2. Stepping back to WooCommerce 3.2.4 allow the site to function but was a bit slow. The combination of WooCommerce 3.2.6 and WordPress 4.8.3 also worked.
Cornforth Images is an image intensive site as it features photography, so more resources would be required than on many other sites. The first solution I tried was an image optimization plugin but the site owner felt the resulting quality was too low.
The next step was to look into PHP 7 which can handle resources more efficiently. The site is hosted on WPEngine which has PHP 7 support. The host also has a plugin that scans active themes and plugins for PHP 7 compatibility. I ran the scan and determined that Cornforth Images was ready for the PHP 7 upgrade.
Once PHP 7 was running, I updated to the latest version of WooCommerce. Not only does the site work, it is noticeably faster than under PHP 5.6.