What populates/updates the SLA Due field in the Task form?

[Maciej Domagals]

My client has requested a custom field that behaves like the OOTB sla_due field in the Incident form. 
The OOTB field updates ONLY when the old SLA Engine is enabled, and the customer wants it to be disabled.
So I tried using the field watcher, but nothing came out.

Is there a Workflow/BR something else that updates the field, which does not appear in the watcher? Because I wanted to copy this functionality over to a new field.

(the picture shows what happens after enabling the legacy engine temporarily)

[jMarshal]

We're not using it...but I found an oob one in Flow Designer called "Default SLA Flow", this is probably where you'll need to add the custom step to update that variable (near the very beginning, likely)

[Maciej Domagals]

There is no step that updates the OOTB due date field anywhere in this flow or workflow of the same name. I'm still stumped, because this field is not updated in any BR or Script Include 😞 tried looking for sla_due and com.snc.sla.run_old_sla_engine in both of these tables, and couldn't find anything that helps.