Were the downgrades done at a Service Center, when they have more control over the upgrade process and can force specific versions to be installed?
A long-standing feature request has been the ability to "roll back" to a previous firmware version. Since Tesla often misses obvious bugs and design flaws in new releases. providing owners the ability to "roll back" to the previous stable release would give more control back to the owners - if they don't like how a new release is working, they can go back to the previous stable release.
Having Tesla test rolling back to arbitrary previous versions could be a nightmare to test. But rolling back to a specific previous version should be something that Tesla and their hand-picked beta testers ought to be able to do with each new release.