Contacts+ stores your contacts information along with any changes and modifications from the last few months (depending on your plan).
This allows you to restore your account to a previous date in case some catastrophe deleted or messed up your address book information on any of your connected accounts, and then Contacts+ sync will make sure to sync that new state to all your connected accounts.
This protects you from accidental or malicious changes done to your contacts, and even issues resulting from software bugs.
However restoring an account to a previous date may result in some recent data loss, and is not a great experience, for that we've created the new Data Protection Service which detects mass deletion sync attempts, blocks them from syncing into your Contacts+ account, and from affecting your other sync sources.
If such an event is detected and the Detect and prevent sync of mass deletion events setting is enabled, Data Protection Service will turn off sync with the offending sync source and alert you via email to either manually allow the deletions to pass through if they are intentional, or will give you a chance to correct the deletions on the source sync account and then re-enable sync.
The service is currently disabled by default and needs to be enabled here: https://app.contactsplus.com/assistant/preferences
This new service is a part of our fix to the Tags mass-deletion issue affecting some of Contacts+ accounts, you can read more about it here.
Please contact us with any questions or feedback.