Variation Swatches causing severe performance issues

Hello, I have set a new site up with Variation Swatches Pro. I have found it is making the site very slow with page loads as long as sixteen seconds. Even pages not using the products are affected. My WP_Debug log shows the following error:

 

[21-Jun-2021 20:18:37 UTC] PHP Fatal error: Uncaught Error: Call to undefined method WC_Product_Variation::get_available_variations() in /srv/htdocs/wp-content/plugins/woo-variation-swatches-pro/includes/functions.php:67
Stack trace:
#0 /wordpress/core/5.7.2/wp-includes/class-wp-hook.php(292): wvs_pro_get_available_variations(”)
#1 /wordpress/core/5.7.2/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(”, Array)
#2 /wordpress/core/5.7.2/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#3 /srv/htdocs/wp-content/plugins/woocommerce/includes/class-wc-ajax.php(90): do_action(‘wc_ajax_get_var…’)
#4 /wordpress/core/5.7.2/wp-includes/class-wp-hook.php(292): WC_AJAX::do_wc_ajax(”)
#5 /wordpress/core/5.7.2/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(false, Array)
#6 /wordpress/core/5.7.2/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#7 /wordpress/core/5.7.2/wp-includes/template-loader.php(13): do_action(‘template_redire…’)
#8 /wordpress/core/5.7.2/wp-blog-header.php(19): require_once(‘/wordpress/core…’)
#9 /wordpress/core/5.7.2/index.php(17): require(‘/wordpress/core…’)
#10 {main}
thrown in /srv/htdocs/wp-content/plugins/woo-variation-swatches-pro/includes/functions.php on line 67

 

I have had to disable Variation Swatches. The conflict is with a theme called Rey. I noticed that if I switch to Storefront, it also runs more slowly than normal with Variation Swatches enabled.