PROBLEM

Replication has failed on this virtual machine because the source VM's virtual disk has been resized. This is an unsupported scenario and replication for this VM must be restarted. Kindly refer to the Knowledge Base article below for more information. (Error code 'REPLICATIONSERVICE_009')

CAUSE

One or more virtual disks for the virtual machine have been resized. This happens if you 'Expand' or 'Shrink' the virtual disk. For 'Dynamically Expanding' or 'Thin Provisioned' virtual disks it will only fail if you increase/decrease the Maximum size limit.

SOLUTION

Replication needs to be restarted for such VMs. In order to restart the replication job for a particular VM, you can follow the guide here.