In article addon set 4 columns, and 4 or more articles to display, then use this custom CSS
.sppb-addon-articles .sppb-col-sm-3:first-child {
width:100%;
float:none;
display:block;
-ms-flex: 0 0 100%;
flex: 0 0 100%;
max-width: 100%;
}
@media (min-width: 768px) {
.sppb-addon-articles .sppb-col-sm-3 {width:33%;
-ms-flex: 0 0 33%;
flex: 0 0 33%;
max-width: 33%;}
}
Final effect