Hi,
The message from the log you posted is not complete but I imagined that the database that could not be backed up is Sogo (same error as in my environment).
Basically, Zentyal creates two databases in Mysql:
1. 'zentyal', which is created by the zentyal-core package.
2. 'sogo', which is created by the Webmail module.
As far as I know, this issue only affects the webmail database.
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