Here I found this from an email thread.
The bottom red comment box does not work, since the “struct” reference from the “Get” is actually a value not a reference. It is very misleading though because the “struct ref” pin even has the ‘by-ref’ diamond shape. But for that to work, a reference needs to be connected as well.
In this case I just re-make the whole struct element and do “set element” individually. If you need to do this nested, you may need to rebuild the entire sub array first using a temp array as I said above.