It has worked in that configuration in the past and I’m pretty certain with the WooCommerce 3.x upgrades I tested that exact configuration. Can you take screenshots of your product setup?

If I mark a product as “Variable Product” and mark “Enable stock management at product level”, what happens is that the stock is now managed by the standard Woocommerce script. It’s as if the plugin was disabled in this case.
If you want to try a quick fix out, edit woocommerce-cart-stock-reducer/includes/class-woocommerce-cart-stock-reducer.php line 972 from:
$stock = $product->get_stock_quantity( ‘edit’ );
to:
$stock = $product->get_stock_quantity( ‘view’ );
Though it’s possible some other issues will pop up because of the change. I’m away on vacation now, but when I get a chance I’ll explore the issue more.
worked perfectly. Thank you very much for the support.
After testing that is not a complete proper fix, it causes other issues. I did just commit a change that should take care of it. I’ve got a few other things to fix up before releasing a new version.