In case it's helpful, I thought I would share our code which triggers this. Perhaps there is a different, thread-safe way to re-initialize logback on a running system that I just don't know about?

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public void reconfigureLogback(URL logbackFile) {

    //Assume SLF4J is bound to logback in the current environment
    LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();
    JoranConfigurator configurator = new JoranConfigurator();
    configurator.setContext(context);

    //Clear any previous configuration (e.g. the default)
    context.reset();

    //Add the application specific properties to the context so that they can be referenced in the logback configuration
    Properties extraProperties = getApplicationProperties();
    for (Map.Entry<Object, Object> entry : extraProperties.entrySet()) {
    
        // ******** BEGIN FAILURE ********
        // This call fails intermittently with a java.util.ConcurrentModificationException
        // This is caused because LoggerContext.putProperty() called LoggerContext.syncRemoteView which
        // iterates through the LoggerContext.loggerCache. Simultaneously, other threads are still calling
        // LoggerContext.getLogger() which can modify the LoggerContext.loggerCache
        
        context.putProperty((String) entry.getKey(), (String) entry.getValue());
        
        // ******** END FAILURE ********
    }

    //Reconfigure logback with the new configuration file
    configurator.doConfigure(logbackFile);
}

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