"The origin server did not find a current representation for the target resource or is not willing to disclose that one exists" upgrading to 12.7

[vmassol]

Seems you have the Java security manager turned on for Tomcat. Maybe see https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Installation/InstallationWAR/InstallationTomcat/#HPolicyconfiguration and https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Installation/InstallationWAR/InstallationTomcat/#HJavaSecurityManager