Oh dear. Yes that is indeed what is causing it. The docs say you can either add the subgroup column and leave it blank, or you can omit it entirely and it'll be fine. However that last part is false. The code on the homepage that guards against the lookup being missing entirely, has a bug. If it sees an existing lookup without all four fields- number, name, group and subgroup, then it throws away the existing rows.
I'll update the top of my answer with the options you have to fix or workaround.
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