When logback.xml configures a scan period it starts a repeating thread ReconfigureOnChangeTask using context.getScheduledExecutorService().

When starting a SocketAppender it uses the same getContext().getScheduledExecutorService() (in AbstractSocketAppender) to run the background Thread. 

Unfortuntely, this scheduledExecutorService has only one thread in its core pool and cannot add additional workers. So when starting the socketAppender the ReconfigureOnChangeTask  is blocked an will never check the configuration file for updates.