RPM dropped: segment first or change layout?

A publisher question about whether RPM drops need segmentation before ad layout changes.

When RPM drops, it is tempting to move ad units immediately. But the drop might be country mix, mobile share, traffic source, ad coverage, consent rate, seasonality, or one template. I think a small triage packet should come first unless a recent layout edit clearly aligns with the drop. For publishers, what is your threshold for changing layout before segmentation is complete?