I have now also tested a small, three person household in County Antrim.
That household isn't showing any random others, however, there is a different, major issue. For all three, it is showing random County/Country of Origin entries.
One has Belfast, one Belfast City and one has County of Cork, when all three on the actual image are Antrim. It correctly shows Antrim on original site.
In a nearby, related household, with 7 occupants, the results correctly have six showing as Co Antrim, but one incorrectly showing as Whitehouse, Co Antrim. All seven are Co Antrim on image.
Methinks I should not bother running any more tests at present.