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
@@ -1306,12 +1306,12 @@
             $paragraphs_entity->set($langcode_key, $form_state->get('langcode'));
           }
         }
-        if (isset($item['subform'])) {
+        if (isset($item['behavior_plugins'])) {
           // Submit all enabled behavior plugins.
           $paragraphs_type = $paragraphs_entity->getParagraphType();
           foreach ($paragraphs_type->getEnabledBehaviorPlugins() as $plugin_id => $plugin_values) {
-            if (!isset($item['subform'][$plugin_id])) {
-              $item['subform'][$plugin_id] = [];
+            if (!isset($item['behavior_plugins'][$plugin_id])) {
+              $item['behavior_plugins'][$plugin_id] = [];
             }
             if (isset($element[$delta]) && isset($element[$delta]['behavior_plugins'][$plugin_id]) && $form_state->getCompleteForm()) {
               $subform_state = SubformState::createForSubform($element[$delta]['behavior_plugins'][$plugin_id], $form_state->getCompleteForm(), $form_state);