You may not be able to add a VM to the replication which was restored from backup.
You may see this error message when you configure the VM to the replication: Unable to configure replication for virtual machine '###' because the virtual machine is already replicated. Cannot create group '###'. Operation ID: fb####47-####-###-85b1-###-d8b#######160
This issue may occur while you are replicating a VM within the same vCenter.
vSphere Replication 8.x
vSphere Replication 9.x
The restored VM still had paused replication settings from before, so vSphere Replication saw it as already configured, blocking the new replication setup.
For example:
vim-cmd vmsvc/getallvms | grep -i VM_Name
vim-cmd hbrsvc/vmreplica.getState
(ID from step 2) vim-cmd hbrsvc/vmreplica.disable
(ID from step 2)