Purview disposition not triggered for SPO documents even after 15 days post-approval

Question

The Context:

Our organization is currently testing disposition of content that was applied a retention label via a Graph API endpoint (driveItem: setRententionLabel). This is the configuration for the retention label file plan:

The reasoning behind labeling our documents as "Record" is because we would like to have proof of disposition once the document is destroyed by Purview:

Additionally, this file plan has been applied to several auto-apply label policies as well. The policies are set in the same SPO site as our Graph API testing scenario here. However, I don't believe that matters anyways since in the endpoint documentation, it clearly states that "(r)etention labels don't need to be published in a retention label policy to be applied using this method":

The Problem:

We were able to successfully apply the retention label, and the items predictably proceed to disposition review after retention period is complete (2 days). Our reviewers then approved the disposition. However, Purview has not yet delete the items, even after the maximum 15 days post-approval window:

Any insight as to why Purview seems quite inconsistent and unreliable in its disposition process is greatly appreciated, thank you.