A rogue device is when the controller detects another wireless network that is broadcasting the same wireless name as the one you have configured on your site. A rogue device can normally be a wireless access point or router.
You can check the rogue device details on the insights page within the controller (on the drop down option Neighbouring Access Points). If the rogue device is part of your network and you know the unit, you can mark it as 'known' on the controller. This will disregard any future alerts being sent to you.
If you are not aware of the Rogue device, please contact us and we will investigate it further for you.