diff --git a/core/lib/Drupal/Core/Plugin/DefaultLazyPluginCollection.php b/core/lib/Drupal/Core/Plugin/DefaultLazyPluginCollection.php
index 00392c3..61702a0 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultLazyPluginCollection.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultLazyPluginCollection.php
@@ -133,14 +133,18 @@ public function getConfiguration() {
    * {@inheritdoc}
    */
   public function setConfiguration($configuration) {
-    $instance_ids = $this->getInstanceIds();
+    // Track each instance ID as it is updated.
+    $unprocessed_instance_ids = $this->getInstanceIds();
+
     foreach ($configuration as $instance_id => $instance_configuration) {
       $this->setInstanceConfiguration($instance_id, $instance_configuration);
-      unset($instance_ids[$instance_id]);
+      // Remove this instance ID from the list being updated.
+      unset($unprocessed_instance_ids[$instance_id]);
     }
-    // Ensure that instances that are no longer configured are removed.
-    foreach ($instance_ids as $instance_id) {
-      $this->removeInstanceId($instance_id);
+
+    // Remove remaining instances that had no configuration specified for them.
+    foreach ($unprocessed_instance_ids as $unprocessed_instance_id) {
+      $this->removeInstanceId($unprocessed_instance_id);
     }
     return $this;
   }