On closer scrutiny, this does appear to be a coincidence or interaction effect between the site’s theme and the WooCommerce pages.
The nature of the error appears to be that the property mainContentOfPage is rendering as structured data with a superfluous set of quotation marks around it. Observe the attributes of the page’s theme-generated container div, which renders into:
id=”theme-page” class=”master-holder clearfix” role=”"main"” itemprop=”"mainContentOfPage"”
