I thought I was dealing with the same problem until I understood how the plugin works, which is different from the others. In the TOOLS – Core Rollback section, select the desired version (e.g. 6.6.2) and click the button to confirm your choice. You’ll get the impression that nothing’s happening… in fact you need now to go to the update page, and the option to reinstall version 6.6.2 will be available among the system update buttons.
I’m sorry but I built the plugin in a local dev environment and it continues to work.
As for the plugin not working, I hope you realize that after selecting the version you wish to rollback to the plugin redirects you to the update-core.php page where the Re-install button now shows you the version you’ve selected. Click it.
