Commvault only using one of 4 available drives

I came to a client recently that had a large backlog of aux copy data and problematic tape libraries. After some remediation I got the tape copy running on 3 drives while awaiting replacements for a couple of broken ones. The replacements were done and following the resumption of the backup the tape copy job will only select one drive. So there are 2 media agents, each with a tape library attached, one has 3 drives and the other has 2 drives, so 5 in total. The storage policy has the 2 libraries in the path and 5 streams with multiplexing x 25. The drive pools on both libraries are set to use all drives. I cannot understand why it will only use a single drive since the backup job was resumed where it was using 3 previously. It now has 5 working drives which can all be seen in Commvault and all work fine in the Tape library GUI’s tests.Commvault version is v11.32.115.