Plugin still works with WordPress 4.9.6 for its intended purpose of allowing multiple author accounts with same email for posting page/post content in WordPress.
So
author - Joe Smith > [email protected]
editor - Customer Support > [email protected]
It’s not intended to allow WooCommerce users to have multiple accounts with same email, as that is not allowed (by design) by the WooCommerce system for tracking “orders” and “customers.” This stops, for example, same customer creating multiple accounts and getting/re-using coupons, or issues with ‘recover password’ (which password?).
So, you would need entirely different solution to allow that behavior in WooCommerce as those are custom post types outside the ‘normal’ user/author functions of WordPress.
If plugin not working while WooCommerce is active, but works with WC ‘off’ — check for plugin/extension conflicts. If WC breaks the plugin for use on main part of site, put in support/ticket for WC. Or check error log/debug in WP for possible issues.
Hope that helps somebody. (I am not plugin author.)