Fancy Product Designer Multistep Product Configurator
Problem -- and simple solution.
The introduction of the responsive product media image in wordpress 'srcset' attribute has started to interfere with the loading of product custom images in the woocommerce custom product image display screens.
To correct for this is simple as a short term solution :
2) add the following code on the product or page on which you want to re-enable product custom images
-- this has re-enabled an essential feature on my pages.