Add-ons that require "open web UI" do not work. "Site cannot be reached"

I have hass.io set up as well as Home Assistant Cloud (which I think is causing the issue).

Any hass.io addons that require a web UI to set up, such as Unifi and backup to google drive, are unable to load the required web ui, it just gives me “site cannot be reached”.

I get this when accessing hass.io via the cloud URL, as well as locally via hassio.local:8123.

Any ideas what is going on and how to fix it?