Patch to fix the bug :
woo-custom-stock-status/includes/class-wc-stock-base.php
case ‘low_amount’ :
// if ( $this_obj->get_stock_quantity() <= get_option( ‘woocommerce_notify_low_stock_amount’ ) ) {
replace by
if ( $this_obj->get_stock_quantity() <= $this_obj->get_low_stock_amount()) {