Linked trigger of "Submit" button not called

I am calling doc.submit() for “Doctype 1” from “Submit” button from “Doctype 2”. And there is a Doctype 3 which is also linked to" Doctype 1" “Submit” trigger.
This issue is when “Submit” is called from “Doctype 2”, Doctype 1 gets Submitted. but the Linked trigger from the “Submit” of Doctype 1 i.e submitting Doctype 3 – This is not happening.

There must be something I am missing.

use in server side on doctype 2

def on_submit(self):