I got this working by doing the following: 1. specifying the arguments in the add_entry line, e.g.

$cron->add_entry("0 5 * * *",
                 {'subroutine' => \&TestSub,
                  'arguments' => [ ],
                  }
                );
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2. Reverting back to a "Log" subroutine, since for some reason, the $log_method wasn't working for me.