No add to cart button after upgrade on variations

Without a link to the site there is very little anyone can suggest.

Sorry, this is an example page.. https://www.parkgatemobility.co.uk/shop/footwear-and-foot-care/ladies-footwear/fabric-shoes/koryl-fabric-shoes/

Likely due to this JS error on your page:

https://dl.dropboxusercontent.com/s/z0fdavw2o62d5mj/2015-08-11%20at%2011.56.png?dl=0

Don’t suppose any one knows how to fix? I am struggling.

You need to find out if its a plugin or the theme loading the datatables script which is erroring.

Hi any solution how got back the button ?

Disable all plugins it will come back. Reactivate 1 plugin at a time until it breaks then you’ll know the culprit.