Feature loss could happen whenever the account is moved from a higher plan to any lower plan in the plans & billing section.
https://www.freshworks.com/freshdesk/helpdesk-features/
In the above link, the plans are displayed in increasing order. When we update an account to a lower plan, the features not part of the chosen plan will be removed from the account, resulting in the feature loss. This is an irreversible action. Once the feature is removed from the account, its related configurations in the account will also be removed.
Even if the account is upgraded immediately after a downgrade, we cannot restore the older settings.
Configuration loss could happen when a specific feature is removed from the account. Also, if any configuration is manually removed, for example, Deleting a field, Deleting an automation rule, Deleting a portal, Deleting a group etc., the configurations will be lost and not be possible to restore them back.
We do not have any option (even from the backend) to restore the configurations once they are lost.