A backup chain gets broken if you perform any of the following operations:
Delete a snapshot
Revert to a snapshot
Create a snapshot without involving Data Protector
Change snapshot handling mode
Add a new virtual machine disk or rename an existing one
Restore the virtual machine
Enable changed block tracking
After completing any of the above operations, you must first run a full backup to start a new backup chain. If you run a session for an incremental backup or a differential backup instead, Data Protector switches the effective backup type in the session to full.