I decided not to bump https://github.community/t5/How-to-use-Git-and-GitHub/x-commits-to-master-since-this-release-is-missing/m-p/3705 because it’s so old, but the issue is still present.
Either this feature was removed for new releases some time in the last 2 weeks or so (I have a release from 20 days ago that still shows this), or it’s related to something else.
Does GitHub only show “x commits to [branch] since this release” when the release was created from a branch, not a specific commit? In my release workflows, it’s very convenient to click the “x commits” link to see a comparison between that tag and the branch head, because that commit list is immediately usable to write the changelog entry for the next version. I’ll have to stop pointing releases to specific commits if this is the case.