After attempting several things including restarting Networker services on storage nodes and Networker server. Disabling and Enabling tape drives. Depositing tapes into the tape drives and running a backup and even resetting tape library. It turns out was the issue was with communication between the storage node and the Data Domain. It wasn't reading the data to be cloned. So after restarting the network service on the storage node, it was able to run and complete the cloning to tape.
Have a Networker environment, in which there's backup to Data Domain, and cloning to a tape library. The backup runs and completes successfully. However, when it comes to the cloning to tape, the backup hangs and doesn't start. The tapes are loaded and mounted successfully, but no writing is done. There are no visible error messages. The status stays on 'Ready for writing, done' . But no writing starts. Have attempted restarting Networker services on the storage node, and the Networker server. Even reset the tape library. Still not able to write. Any thoughts on how I can fix that. It's Networker 18.2.  
Networker Unable to clone to tape even when tape is mounted