OracleDependency 无法通知

C# 应用OracleDependency通知数据库变化例子：
OracleCommand cmd = new OracleCommand(sql, _con);
_dep = new OracleDependency(cmd);

cmd.Notification.IsNotifiedOnce = false; ;
cmd.Notification.Timeout = 0;
cmd.Notification.IsPersistent = true;

 _dep.OnChange += new OnChangeEventHandler(OnDatabaseNotification);
 cmd.ExecuteNonQuery();

应用数据库 oracle11g 驱动：Oracle.DataAccess.dll 2.112.3.0

运行时，DBA_CHANGE_NOTIFICATION_REGS 有注册信息：

当数据库修改时： 注册信息消失
应用程序也接收不到通知，求大神帮助

https://docs.oracle.com/cd/B19306_01/win.102/b14307/featChange.htm
https://stackoverflow.com/questions/11841901/oracledependency-event-is-not-firing