On PR diff views (specifically single-commit PRs, or when viewing a single commit within a PR), the controls to expand collapsed/unmodified lines between hunks are missing, so there's no way to expand surrounding file context inline.
Multi-commit PR ranges still seem to show the expand buttons as expected.
Not 100% sure, but this might be because single-commit diffs stream the .patch payload (processPatch), which only includes the 3-line hunk context (isPartial: true in @pierre/diffs) rather than the full file blobs fetched for multi-commit ranges.
Also when viewing diffs in "split" mode, I feel the "x unmodified lines" text should be centered across both sides of the split, instead of within the left column.
also, this is a recent regression i believe