diff -u b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
--- b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
+++ b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
@@ -611,7 +611,7 @@
         $display->buildForm($paragraphs_entity, $element['subform'], $form_state);
         foreach (Element::children($element['subform']) as $field) {
           if ($paragraphs_entity->hasField($field)) {
-            $element['subform'][$field]['#group'] = 'field_paragraphs_demo][0][subform][paragraph_content';
+            $element['subform'][$field]['#group'] = implode('][', array_merge($element_parents, ['paragraph_content']));
             $translatable = $paragraphs_entity->{$field}->getFieldDefinition()->isTranslatable();
             if ($translatable) {
               $element['subform'][$field]['widget']['#after_build'][] = [
@@ -628,8 +628,7 @@
           foreach ($paragraphs_type->getEnabledBehaviorPlugins() as $plugin_id => $plugin) {
             $element['subform'][$plugin_id] = [
               '#type' => 'container',
-              '#foo' => 'bar',
-              '#group' => 'field_paragraphs_demo][0][subform][paragraph_behavior',
+              '#group' => implode('][', array_merge($element_parents, ['paragraph_behavior'])),
             ];
             $element['subform'][$plugin_id] += (array) $plugin->buildBehaviorForm($paragraphs_entity);
           }