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.