The Security Analytics UI grants the ability to create groups for services. Image description
However, if you try to add the same device to a group twice, it will increment the count, but not add the device. Image description This typically occurs when you refresh the page, then try to add the same device.
This is a minor flaw in the UI that will be patched in an upcoming release of 10.4. In the interim, the workaround referenced in this article may be used.
Refresh the page again to reset the count back to the proper value.