I am also confused by this report. Installing the migration plugin does not install ClassicPress. You posted an error that indicates your site was not succesfully switched over to ClassicPress.
But if you click Update Now button, you get the error I described.
ClassicPress is running and since I downloaded it from the link I don’t think there is an update for it.
Now that I looked at it again, it says I’m running the Alpha version which is what the link downloaded and it says a beta version is available in the update.
Migrating to ClassicPress will show this version number first and then prompt you to upgrade to the beta version. The upgrade prompt may be for the core software itself.
We are working on several options to improve this experience.
The “double upgrade” is fixed in the new version of the migration plugin 0.3.0, which is now available on GitHub.
The version that is installed after migration will be 1.0.0-beta1+migration.20181122. This is a temporary fix, and we will either continue updating this version after each release or come up with a more permanent solution.
@azimpact this is the first report that we’ve had of ClassicPress failing to upgrade itself after migration. Did you see this error every time? Are you still seeing it?