A recurring job from a policy that contains a Duplicate Backup Sets template or a Synthetic Backup template must be run on the same managed media server where the job was initially run. The jobs produced from these templates require access to the media that contains the backup sets that were produced from the preceding jobs.
If you change the target device of the templates within a policy, the jobs resulting from that template can then be delegated to a different managed media server. However, if the destination managed media server is still a valid candidate for delegation, it will be used.
If you do not change the destination devices in the templates, and if the targeted managed media server is unavailable, the jobs remain queued, waiting for the targeted managed media server to become available. If the targeted managed media server is no longer configured as a managed media server, then you can re-delegate the jobs.
About creating jobs using policies and selection lists
Adding a duplicate backup template to a policy
About creating a synthetic backup by copying the example policy