Today I had an unfortunate power outage at my home, therefore my lab was shutdown inadvertently. After powering up my systems again some Ubiquiti devices which were registered with my Unifi Controller had the disconnected status, even though I was able to ping them. After some reboots, and re-adoptions I didn’t get them online. 
Luckily after an hour troubleshooting, and berating I was able to get the devices back online through the following steps:

1. Login to the devices with SSH (I had 2 Access Points and 2 Switches disconnected)
2. Executed the following command: set-inform http://192.168.x.x:8080/inform
3. Refresh the Unifi Controller interface

After issuing the command from the device itself, it re-registered with the Unifi Controller and I was able to manage them from my single pane of glass again!

SDN ROCKSS!!!

*192.168.x.x is my internal IP address for my Unifi Controller.