sometimes we might face to import deletions after adding new synchronization rule.  As you can see here are 167 incoming deletions:

This incoming deletions are not expected. But if we have a look on the latest changed rule we can see this:

This is in-bound rule for the on-prem Active Directory connector and as you can see the selected object type is person. And this is what causing the issue. The correct object type for the connected system object type is user:

Even if the object type for the connected system is changed back, the behavior is still the same and the deletions are still there.

The question how to fix this?

Here is the solution:

1. open the Azure AD Connect Synchronization Service Manager (aka Sync Console)+
2. Click on connector
3. Select the on-prem AD Connector and click on properties 
4. In the window, click on the: Select Object Types. As you will see, the object type: person is selected:
5.  Clear the checkbox and click on OK. 
6. The next full import will add the previously deleted user objects. 

Happy Troubleshooting!