Don't use woocommerce_loaded hook

When using this hook, if woocommerce_loaded is fired before the discount plus is loaded, the plugin doesn’t work at all.

To fix change the line:
add_action( 'woocommerce_loaded', array( $this, 'woocommerce_loaded' ) );

with:
add_action( 'plugins_loaded', array( $this, 'woocommerce_loaded' ) );

and then in public function woocommerce_loaded() {

use
if ( in_array( 'woocommerce/woocommerce.php', apply_filters( 'active_plugins', get_option( 'active_plugins' ))) && get_option( 'woocommerce_enable_plus_discounts', 'yes' ) == 'yes' ) {

instead of

if(get_option( 'woocommerce_enable_plus_discounts', 'yes' ) == 'yes' ) {

and it works.

https://wordpress.org/plugins/woocommerce-discounts-plus/