Getting Error when enabling WooCommerce Email Template Plugin

I have purchased 9Mail + WooCommerce Email customizer both, 9mail is enabled already but once I enable woocommerce plugin for email customizer, the website goes to critical error.

Fatal error: Uncaught Error: Call to a member function get_author_permastruct() on null in /var/www/wp-includes/author-template.php:368 Stack trace: #0 /var/www/wp-content/mu-plugins/gd-system-plugin/includes/class-cache-v2.php(378): get_author_posts_url(2) #1 /var/www/wp-includes/class-wp-hook.php(324): WPaaS\Cache_V2->do_purge(1404, Object(WP_Post)) #2 /var/www/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(’’, Array) #3 /var/www/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #4 /var/www/wp-includes/post.php(7368): do_action(‘clean_post_cach…’, 1404, Object(WP_Post)) #5 /var/www/wp-includes/post.php(4698): clean_post_cache(Object(WP_Post)) #6 /var/www/wp-content/plugins/woocommerce-email-template-customizer/includes/utils.php(659): wp_insert_post(Array) #7 /var/www/wp-content/plugins/woocommerce-email-template-customizer/woocommerce-email-template-customizer.php(91): VIWEC\INCLUDES\Utils::insert_block(‘{“style_contain…’, ‘Header’) #8 /var/www/wp-includes/class-wp-hook.php(324): WooCommerce_Email_Template_Customizer->{closure}(’’) #9 /var/www/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array) #10 /var/www/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #11 /var/www/wp-settings.php(550): do_action(‘plugins_loaded’) #12 /var/www/wp-config.php(102): require_once(’/var/www/wp-set…’) #13 /var/www/wp-load.php(50): require_once(’/var/www/wp-con…’) #14 /var/www/wp-admin/admin.php(34): require_once(’/var/www/wp-loa…’) #15 /var/www/wp-admin/plugins.php(10): require_once(’/var/www/wp-adm…’) #16 {main} thrown in /var/www/wp-includes/author-template.php on line 368

Please fix this asap.