Retention policy is not working

I created retention policy for clear the junk e-mail folder daily. The following is detail setting. I monitoring 1 week but found it's not working. That's mean it haven't clear the email junk e-mail folder. But it's working if I ran the PS Start-ManagedFolderAssistant -Identity <email_address>. So I'm not sure any setup or procedure missed in this retention policy or server.

Created a retention policy tag (tag type: Junk E-mail / age limit for retention: 1 / action: permanently delete)

Created a retention policy (type: Junk E-mail / action: permanently delete / age limit for retention: 1 / retention enabled: true / mailboxes: my testing mailbox)

Thanks!!