VM 2.0.22 generic cart variants not adding to cart

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The latest update appears to have a problem, I am unable to add generic cart variant products to the cart, and the modal popup cart fails to load. it works fine with stockable variants, and simple products. With the popup disabled all works fine.

My test site is joomla 2.11, VM 2.0.22 with the Beez_20 template with no modifications.

Anyone else encountered this or found a solution??