I don't think it is broken ... for some Reason the Upgrader and the Software Updater doesn't work like they should.
Okay, let's try the Following:
sudo apt purge zorin-os-upgrader update-manager
That will uninstall the Zorin OS Upgrader and the Software Updater. Then Type:
sudo apt autoremove
to remove File Rests. But please take a Look at the List of the removable Packages before You delete them. Then reboot. After the Reboot type in the Terminal:
sudo apt install zorin-os-upgrader update-manager
to install both again. And then there is a Point what I didn't mentioned yet: The Upgrader is still in Beta. So, it could be unstable and not working properly. So, before making the Upgrade have backup Your Data and have a Zorin Bootstick ready for the Case something should going bad.
When prepared, type in Terminal:
sudo apt update && sudo apt upgrade to update Your System. Then:
gsettings set com.zorin.desktop.upgrader show-test-upgrades true
And then start the Upgrader.