With Rundeck plugin installed 3.6.7 or 3.6.9 on a the latest LTS 2.277.4 we can not save any changes to the "configure system" UI.  We noted a stack trace in the server logs about rundeck, so we disabled the plugin and verified we are able to resume editing system configs.

While we have a work around that involved disabling the plugin, making the change then enabling the plugin, the plugin should not break core functionality.