Regarding missing metapackages and a few other errors encountered, based on our testing, it appears that they are caused by users attempting to upgrade using an older version of the Upgrade Zorin OS tool. The upgrader should be version 1.3.9 as older versions don't have all the latest bug fixes.
For those encountering issues: please make sure to install all of the latest updates from the Software Updater just before running the upgrader again. We would recommend you to make sure you're carefully following the instructions in our upgrade guide here: