Occasionally the same AP will appear twice in the APs/Devices list. Sometimes all of the information for the device is displayed in each entry; sometimes most of the information is NOT displayed for one of the two entries and the IP address is listed as 10.0.0.0. In both cases a unique ID number (see next paragraph) will be assigned to each instance.
The ID appears at the end of any URL pertaining to a particular device.
Example: The URL for the Monitor page would be something like:
You can try just deleting both duplicates and then re-adding the device. It appears that in some cases duplicates are being caused by CDP (Cisco Discovery Protocol). If you have finished the discovery process, you can try disabling this option as follows...
In the Routers and Switches section of the Groups | Basic page look for the "Read CDP Table for Device Discovery" option, select Disabled from the drop down and click on "Save and Apply".