I received a polite email this evening from a customer saying that they couldn't get to the cart or checkout pages.
Upon further investigation none of the non-product pages work (cart, my a/c, etc). I've turned off all the plugins (even woocommerce at one point which showed the home page instead of the shop page ??) but that doesn't seem to have made a difference. I've recreated all the shop sub-pages which work if they are not a sub-page of 'shop' (ie a parent page in their own right), but not when below 'shop'.