Followup:
We think this may have to do with duplicating fields and moving them to another group.
Inspecting the editor showed us that the duplicated fields on the edit screen have the same slugs, but different ids
In this case, what’s showing up on the post editor is a set of fields we duplicated from another group.
i.e. we get two fields named jv_subheading, but one is field_542228e1ac753
and the other is field_54206f572fbf5