Why is the static value different from appender(log4j custom appender)?

I make static variable like this in spring.

public class A {
  private static final Map<String, Session> listMap = new HashMap<>();
  public static Map<String> getMap() { return this.listMap.values() }
  public static void addMap(String name, Session s) { return this.listMap.put(name, s) }
}

I save in service layer.

@Slf4j
public class BService {
  public void addSession(String name, Session s) { 
    A.addMap("a", s);
    log.info("added!");
  }
}

After saving it, I used it in custom appender.(https://www.baeldung.com/log4j2-custom-appender)

@Plugin(
  name = "MapAppender", 
  category = Core.CATEGORY_NAME, 
  elementType = Appender.ELEMENT_TYPE)
public class MapAppender extends AbstractAppender {

    private ConcurrentMap<String, LogEvent> eventMap = new ConcurrentHashMap<>();

    protected MapAppender(String name, Filter filter) {
        super(name, filter, null);
    }

    @PluginFactory
    public static MapAppender createAppender(
      @PluginAttribute("name") String name, 
      @PluginElement("Filter") Filter filter) {
        return new MapAppender(name, filter);
    }

    @Override
    public void append(LogEvent event) {
        Map<> resultMap = A.getMap();
        send()
    }
}

However, when the appender's append() method is executed, A.getMap() return nothing(size 0). (A.getMap() return correctly in service layer.) Why is the static value different?..

listMap is loaded when you call addSessionso it is empty When append() method is called