After a UXG is installed an adopted to it's home site, next step is normally upgrading the firmware.  If the firmware version is on 1.11 or lower, it will not automatically upgrade from the devices page.  You will have to manually step-up the firmware to get it to the latest versions (3.1.8 at of this article).

To do this, goto the Site Settings, Updates, and disable auto updates.  You will then need to goto the UI Community forums and find the UniFi NeXt-Gen Gateway firmware posts. UI Community Releases. Do a search for the word 'Next' and it will list all of the UXG Firmware posts. Once you have found the versions you need, copy the download link and return to the UniFi site.  Go back to devices and select the UXG and go to the device settings.  Scroll down to 'Manual Firmware Update" and paste the URL into that field and press 'Update'.  The router will begin the firmware process then reboot.  When it re-provisions and comes back online, it should then show the firmware version you pushed.  Repeat as many times as needed to get it to at least version 3.0.7.  From there, you can then go back to the device page and press 'Click to Update' as we normally would.

If you prefer the SSH method:

SSH into your UXG-Pro and execute the following in it's shell (replace <firmware_url> with one of the download links found below):

The firmware order goes as follows:
1.11.0 ->  1.13.0 -> 3.0.7 -> 3.0.8