I have not seen any NetWorker limitation on how many autochangers a storage node can support
Please check your NetWorker autochanger licenses. How many slots does each license support? Also, how many slots are in each jukebox?
What license is assigned to which jukebox? You can find this by opening each NetWorker jukebox property, and see which enabler code is assign to it. It should show the enabler code.
From the hardware perspective, how are the jukeboxes and drives connected to the NetWorker storage node? What type of controller is being used? How many controllers? What type of cable? If the jukebox and drives have a SCSI interface, check what type it is. Single ended? Wide? Differential? Fiber? Does the cable, connector, and controller all use the same interface type? Did you check the hardware compatibility matrix to see if all the hardware is compatible and supported?
Describe how each jukebox and drives are connected to the host. Are they all daisy chained together? What are the cable lengths? If there is a connectivity issue, then you should be able to see issues in the operating system logs. Look for any SCSI or I/O errors related to your jukebox, tape drives, and controllers, as well as any device disconnects.
If only one jukebox is physically connected, does it work ok?