If scheduled jobs are run individually nothing is logged to civicrm job log
When running scheduled jobs individually to have greater control over the timing or parameters of those jobs then nothing is logged to the JobLog at least for certain jobs like process_mailing. This leaves the user to implement something else for logging.
I don't agree with this approach because it will push organisations to use custom solutions but it should at least be a documented limitation.
https://docs.civicrm.org/user/en/latest/initial-set-up/scheduled-jobs/#specific-jobs
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