I have a hypothesis about how their system operates. It appears that their approach might prioritize reviewing new applications first to process the maximum number of applications. Therefore, the examination of documents submitted in response to an Additional Document Request (ADR) might be delayed until closer to the end of the specified deadline in the ADR (which can be 7 days for some applicants, 30 days for others).
They seem not to have an immediate trigger mechanism indicating that a specific individual has submitted the requested documents and they need to be reviewed urgently. Rather, there seems to be a trigger associated with the deadline for document submission. The case is likely revisited after ADR closer to the end of the deadline, either to review the already submitted documents or, if the documents are not provided, to reject the application.
So, a bunch of things here. Each stage (e.g. criminality) has a due date assigned to it, but at times ADR in itself is a sub-section of criminality, security, background, etc so a due date isn't assigned to the ADR submission itself.
Here's an ADR/typical change received example from a GCMS note:
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NOTES:8
Created Date: 2023/02/28 16:17:06
Created By: MM00507
Updated Date: 2023/02/28 16:17:40
Updated By: MM00507
restricted: No
Label: Client Enquiry
Office: Central Intake office
Text: Change in Marital Status - Married Email received via GMCS (Provided Report) via Call Centre. Review Required. Advising change in marital status- married. NO response provided.
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Notice how there's no due date to it. But as a result of this, an updated due date will be assigned to the eligibility. Important to know that Case processing agents can decide whether they'd like to honor these due dates or not.