Sometimes the upgrades don't work from the Unifi console, but you can still update them via CLI over SSH. For me, the upgrade command wouldn't pull the tar file from the site, so I had to push it via SSH/SCP.
1) Download the software
From MAC terminal or Linux (Windows, download from vendor site and use winscp):
scp UGW4.v188.8.131.5218769 [email protected]<router IP>:~
Looks like this:
2) Upgrade firmware
From the router:
Afterwards, you will see it progressing and then it will warn you that it's going to reboot. This took only a few seconds for my device.
You can confirm the new version from the Unifi web console:
Most likely, the reason it wouldn't upgrade from the console for me (it upgraded the AP PRO and Switch 48 just fine) is that I have an issue with my SPF+ port where each time my switch power cycles, I have to re-seat the GBIC.