There's a few different places that logging can be configured. Here are a few:
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In the GUI under System - Logs. You looked there.
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Some monitors have a debug option that will create a log file in /var/log.
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/etc/syslog-ng/syslog-ng.conf can be edited to produce/alter different logging for different events.
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TMSH DB variables. Do a 'tmsh list sys db | grep log' to see a general list of the different logging variables, and then 'tmsh show sys db [db name]' to show its value. These won't usually create new logs, but mostly control the verbosity of existing logs.