Problem:You've installed a Unifi AP system and though things were working at one point, they now are not.
Solution:Open port 8080 on your unifi controller.
Other solutions:Make sure the devices can find your DNS server and resolve the controller correctly.
You can SSH into the devices and read their logs.
You can replace the hostname with the hostIP if that's what's failing, or as a test.
Edit; this especially applies if you've moved the software to run as a service - as when the java applet opens it opens the firewall's ports.
You may need to set-inform on the device, and point it to the IP address or name of server. You can also config eth to ensure that the device is set to the correct IP
Keep in mind, either it's using the old admin PW as the SSH password, or if it's updated to a newer controller, it's using a special SSH key which can be found in your controller, as the password for SSH.