Cannot select VMware guest for backup when on a vDS

Hi - we have been successfully backing up VMware guests with the EBR for two years.

I am just in the process of migrating our VMware host networking from standard switches to vDS.

I can move a guest from a standard switch to vDS and the VM continues to operate normally - VM networking is fine,

If I then use the vSphere Web Client to edit the backup policy to select the guest, the EBR plug-in shows the clock symbol and never completes the action. The only option then is to close the vSphere Web Client completely.

I do not understand why the change in guest networking would stop the ability to include the guest in a backup job? I have been unable to find any issues like this in the community or knowledge base - presumably because it should not be an issue.

Any suggestions would be much appreciated!