WordPress Speed Up Service | WordPress Website Maintenance Packages Reply To: Letters being added to end of plugin JS/CSS files, by robhsc I’ve managed to fix this now. I’ve switched off the domain mapping plugin and used the native mapping feature which was included from WP 4.5+. I’ve also had to set the Site Address (URL), the Siteurl and the Home to the mapped domain name. Previously I had it on the subdomain from the primary site. Thanks Rob Reply To: Letters being added to end of plugin JS/CSS files