Hey,
Working for me (frappe v13.14.0, ERPNext v13.14.1), i think it was a problem of misunderstanding how Deferred Accounting worked, i invite your to read the documentation about Deferred Accounting again, and try it manually before trying to do it automatically. It is important that the service start date and end date corresponds with data in your sales invoice.
Hope it could help,
Sincerely yours,
Martin