In some 0.7 installations drag drop does work much less easy than in 0.6.
0.6 uses: jQuery UI Sortable
0.7 uses: http://johnny.github.io/jquery-sortable/
jQuery UI 1.12 has 4 bugfixes for the Sortable component. It might be possible now to go back to jQuery UI.
Use jQuery UI Sortable again
Make sure jquery UI is in the template:
<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"></script>