When I add a new Oracle Monitor, the monitor is added successfully but I see two Oracle Monitors added in the web client for the same Oracle server. Reason:
When you add a Oracle Monitor, Applications Manager discovers the Oracle database server and adds a Oracle Monitor. Additionally, it also adds another Monitor for the particular instance of the Oracle database that you have configured. By this feature you can monitor each instance of the same Oracle database.
Solution:
The extra Oracle Monitor that is displayed in the client is harmless. You can simply retain the Oracle Database Monitor for the the instance and delete the other Monitor.