Matomo encountered an error: Uncaught Error: Class "Piwik\Plugins\CustomVariables\CustomVariables" not found in /var/www/piwik/core/Tracker/TrackerCodeGenerator.php:98 Stack trace: #0 /var/www/piwik/plugins/SitesManager/API.php(159): Piwik\Tracker\TrackerCodeGenerator->generate() #1 [internal function]: Piwik\Plugins\SitesManager\API->getJavascriptTag() #2 /var/www/piwik/core/API/Proxy.php(255): call_user_func_array() #3 /var/www/piwik/core/Context.php(28): Piwik\API\Proxy->Piwik\API\{closure}() #4 /var/www/piwik/core/API/Proxy.php(158): Piwik\Context::executeWithQueryParameters() #5 /var/www/piwik/core/API/Request.php(272): Piwik\API\Proxy->call() #6 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik/Request/Php.php(46): Piwik\API\Request->process() #7 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik/Request/Php.php(18): WP_Piwik\Request\Php->call() #8 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik/Request.php(63): WP_Piwik\Request\Php->request() #9 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik.php(1038): WP_Piwik\Request->perform() #10 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik.php(1205): WP_Piwik->request() #11 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik/TrackingCode.php(16): WP_Piwik->updateTrackingCode() #12 /var/www/thegtricks/wp-content/plugins/wp-piwik/classes/WP_Piwik.php(296): WP_Piwik\TrackingCode->__construct() #13 /var/www/thegtricks/wp-includes/class-wp-hook.php(324): WP_Piwik->addJavascriptCode() #14 /var/www/thegtricks/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters() #15 /var/www/thegtricks/wp-includes/plugin.php(517): WP_Hook->do_action() #16 /var/www/thegtricks/wp-includes/general-template.php(3066): do_action() #17 /var/www/thegtricks/wp-content/themes/twentyfifteen-child/footer.php(45): wp_footer() #18 /var/www/thegtricks/wp-includes/template.php(810): require_once('...') #19 /var/www/thegtricks/wp-includes/template.php(745): load_template() #20 /var/www/thegtricks/wp-includes/general-template.php(92): locate_template() #21 /var/www/thegtricks/wp-content/themes/twentyfifteen/archive.php(68): get_footer() #22 /var/www/thegtricks/wp-includes/template-loader.php(106): include('...') #23 /var/www/thegtricks/wp-blog-header.php(19): require_once('...') #24 /var/www/thegtricks/index.php(17): require('...') #25 {main} thrown (which lead to: Session must be started before any output has been sent to the browser; output started in /var/www/thegtricks/wp-includes/class-wp-styles.php/290)