Variation of https://www.drupal.org/node/2853973 for the case when https://www.drupal.org/node/2853167 is already applied

draggableviews-relationship-2853973-X-D8.patch

diff --git a/src/Plugin/views/field/DraggableViewsField.php b/src/Plugin/views/field/DraggableViewsField.php
index bfade16..93c4420 100755
--- a/src/Plugin/views/field/DraggableViewsField.php
+++ b/src/Plugin/views/field/DraggableViewsField.php
@@ -62,7 +62,7 @@ class DraggableViewsField extends BulkForm {
       // Item to keep id of the entity.
       $form[$this->options['id']][$row_index]['id'] = array(
         '#type' => 'hidden',
-        '#value' => $row->{$this->definition['entity field']},
+        '#value' => $this->getEntity($row)->id(),
         '#attributes' => array('class' => array('draggableviews-id')),
       );