In 12.6 SAP in their infinite wisdom changed the default byte alignment from 1 to 4 without telling anyone. Eventually it was explained somewhere on the SAP forum but I can't find it. It isn't in the Appeon 2017 documentation either.
There is supposed to be something you can add the the declaration but I forgot what it is. All I remember is that it is a misspelling of a C++ keyword that controls byte alignment. Before Appeon gets around to documenting it, I hope they change it to something easier to remember like ByteAlign(n).