@JNL
Subgroups work on the lowest level, they are convenient as stated. But should not be used in intermediate levels, unless used in conjunction with "deep make unique" or similar extensions.
Can drive from parent, the red may show a non-initiated attribute. Though shows "0" in grey, the value in parent is null. So, enter a value.
Otherwise, the formula is incorrect or sometimes disconnected.
Please upload any problem DCs