This is actually a bug in the TicketTable login. We check if the ticket is allowed to be private by doing permissions checks even when the self::$noPermissionsCheck flag is set because we're managing tickets outside of a user session – as is the case with the auto-close plugin.
Edit administrator/components/com_ats/src/Table/TicketTable.php and change line 849 to read:
if (!self::$noPermissionsCheck && !$this->public)
I will include this bug fix in the next release.
Nicholas K. Dionysopoulos
Lead Developer and Director
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