Archiving error 3: tape is being mounted and unmounted too often

The tape gets mounted and unmounted a lot during transfers.  Why?

Here is a diagram from Chris Prosser / Brian Davies:

<img width="1782" height="86" alt="Image" src="https://github.com/user-attachments/assets/9a0f1e7f-9c61-4314-870a-2da1fac37979" />