Update of security update hangs for Mojave 10.14.6
I did figure out the culprit was a piece of software that was loaded using LaunchDaemons that somehow prevented a clean shutdown or startup. After backing up and deleting the LaunchDaemon files the update could be installed without any problems.
I could find more infos on the website: https://helpcenter.graphisoft.com/knowledgebase/75010/