Hello, Matteo: is it possible your disk volumes are becoming Full within 1 minute, and them Bacula tries to create again a volume with a non-unique name? This may happen if your disk is full or if it is a multi-volume backup.
Even using JobID variable it's not guaranteed you will have unique LabelFormat naming generation. I would add (v.g.) NumVols variable.
Also, there is no need to you "Maximum Volume Jobs = 1" and "Use Volume _Once_ = yes" both. And the first one is better.
Regards,
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