Plugin stopped working

All products (on all of my websites with the plugin) stopped working (some time ago) as they should. You can select one option and then the other options disappear / are not selectable. A lot of products are not available while they should be . Also there is a error “DISABLE_WP_CRON config setting set to true, please change to false otherwise some features may not work as expected” when i want to bulk add products.

The page I need help with: [log in to see the link]