Undefined variable $price_valid_until

Hi,

We’re experiencing regular errors with – we think – this plugin. Stack trace as follows:

Error message
Undefined variable $price_valid_until
Stack Trace
New
in Rex_Product_Feed_Pro_Admin::wpfm_structured_data called at /nas/content/live/oursite/wp-includes/class-wp-hook.php (308)
in WP_Hook::apply_filters called at /nas/content/live/oursite/wp-includes/plugin.php (205)
in apply_filters called at /nas/content/live/oursite/wp-content/plugins/woocommerce/includes/class-wc-structured-data.php (328)
in WC_Structured_Data::generate_product_data called at /nas/content/live/oursite/wp-includes/class-wp-hook.php (308)
in WP_Hook::apply_filters called at /nas/content/live/oursite/wp-includes/class-wp-hook.php (332)
in WP_Hook::do_action called at /nas/content/live/oursite/wp-includes/plugin.php (517)
in do_action called at /nas/content/live/oursite/wp-content/themes/storefront-child/woocommerce/content-single-product.php (78)
in require called at /nas/content/live/oursite/wp-includes/template.php (785)
in load_template called at /nas/content/live/oursite/wp-content/plugins/woocommerce/includes/wc-core-functions.php (284)
in wc_get_template_part called at /nas/content/live/oursite/wp-content/themes/storefront-child/woocommerce/single-product.php (43)
in include called at /nas/content/live/oursite/wp-includes/template-loader.php (106)
in require_once called at /nas/content/live/oursite/wp-blog-header.php (19)
in require called at /nas/content/live/oursite/index.php (17)

Granted, it’s an E_WARNING, but even excessive E_WARNINGS hurt response time. We’re getting this about 3000 times in a 5 hour window. None of the feeds explicitly reference this variable.

Any help in diagnosing this would be greatly appreciated.