I also have a strange Drag&Drop reset issue:
On my localhost installation d&d is working fine but on the remote system - same configuration (SortableDataObject::add_sortable_classes() is set in _config.php) after Save&Publish the SortOrder is reset.
My current Version is SS 2.4.5 with DOM r540
addition: There are 2 sortable DataObjects. For one of them d&d is working.
I have no idea what I may have done wrong.