reverted:
--- b/commerce.services.yml
+++ a/commerce.services.yml
@@ -64,10 +64,3 @@
   plugin.manager.commerce_entity_trait:
     class: Drupal\commerce\EntityTraitManager
     arguments: ['@container.namespaces', '@cache.discovery', '@module_handler', '@commerce.configurable_field_manager']
-  serializer.normalizer.object:
-    class: Drupal\commerce\Normalizer\ObjectAnyNormalizer
-    tags:
-    # This normalizer must be higher than serializer.normalizer.typed_data
-    # So setting priority as 0 here.
-    # @see \Drupal\commerce\Normalizer\ObjectAnyNormalizer::supportsNormalization
-      - { name: normalizer, priority: 0}
reverted:
--- b/modules/order/src/Adjustment.php
+++ a/modules/order/src/Adjustment.php
@@ -7,7 +7,7 @@
 /**
  * Represents an adjustment.
  */
+final class Adjustment {
-final class Adjustment implements \IteratorAggregate {
 
   /**
    * The adjustment type.
@@ -196,30 +196,4 @@
     return $this->locked;
   }
 
-  /**
-   * Returns all storage elements as an array.
-   *
-   * @return array
-   *   An associative array of attributes.
-   */
-  public function toArray() {
-    return [
-      'type' => $this->type,
-      'label' => $this->label,
-      'amount' => $this->amount->toArray(),
-      'percentage' => $this->percentage,
-      'sourceId' => $this->sourceId,
-      'included' => $this->included,
-      'locked' => $this->locked,
-    ];
-
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getIterator() {
-    return new \ArrayIterator($this->toArray());
-  }
-
 }
reverted:
--- b/src/Normalizer/ObjectAnyNormalizer.php
+++ /dev/null
@@ -1,50 +0,0 @@
-<?php
-
-namespace Drupal\commerce\Normalizer;
-
-use Drupal\commerce_order\Adjustment;
-use Drupal\serialization\Normalizer\NormalizerBase;
-
-/**
- * Take place of TypedDataNormalizer when any's value is object.
- *
- * Here is for normalizing Adjustment. Delete this normalizer after
- * https://www.drupal.org/node/2915705 be fixed in core.
- */
-class ObjectAnyNormalizer extends NormalizerBase {
-
-  /**
-   * The interface or class that this Normalizer supports.
-   *
-   * @var string
-   */
-  protected $supportedInterfaceOrClass = 'Drupal\Core\TypedData\Plugin\DataType\Any';
-
-  /**
-   * {@inheritdoc}
-   */
-  public function supportsNormalization($data, $format = NULL) {
-    /* @var \Drupal\Core\TypedData\Plugin\DataType\Any $data */
-    if (parent::supportsNormalization($data, $format)) {
-      $value = $data->getValue();
-      if (isset($value) && is_object($value) && $value instanceof Adjustment) {
-        return TRUE;
-      }
-    }
-    return FALSE;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function normalize($object, $format = NULL, array $context = []) {
-    $value = $object->getValue();
-    // If the value is object or array, return the normalized result, object
-    // must be typed data or traversable to be normalizable.
-    if (isset($value) && (is_object($value) || is_array($value))) {
-      $value = $this->serializer->normalize($value, $format, $context);
-    }
-    return $value;
-  }
-
-}
only in patch2:
unchanged:
--- a/modules/order/commerce_order.services.yml
+++ b/modules/order/commerce_order.services.yml
@@ -62,3 +62,10 @@ services:
     arguments: ['@current_route_match']
     tags:
       - { name: commerce_store.store_resolver, priority: 100 }
+  serializer.normalizer.any_adjustment:
+    class: Drupal\commerce_order\Normalizer\AnyAdjustmentNormalizer
+    tags:
+    # This normalizer must be higher than serializer.normalizer.typed_data
+    # So setting priority as 0 here.
+    # @see \Drupal\commerce\Normalizer\ObjectAnyNormalizer::supportsNormalization
+      - { name: normalizer, priority: 0}
only in patch2:
unchanged:
--- /dev/null
+++ b/modules/order/src/Normalizer/AnyAdjustmentNormalizer.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace Drupal\commerce_order\Normalizer;
+
+use Drupal\commerce_order\Adjustment;
+use Drupal\serialization\Normalizer\NormalizerBase;
+
+/**
+ * Custom normalizer for 'any' typed data with Adjustment stored.
+ */
+class AnyAdjustmentNormalizer extends NormalizerBase {
+
+  /**
+   * The interface or class that this Normalizer supports.
+   *
+   * @var string
+   */
+  protected $supportedInterfaceOrClass = 'Drupal\Core\TypedData\Plugin\DataType\Any';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function supportsNormalization($data, $format = NULL) {
+    /* @var \Drupal\Core\TypedData\Plugin\DataType\Any $data */
+    if (parent::supportsNormalization($data, $format)) {
+      $value = $data->getValue();
+      if (isset($value) && is_object($value) && $value instanceof Adjustment) {
+        return TRUE;
+      }
+    }
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function normalize($object, $format = NULL, array $context = []) {
+    $attributes = [];
+    /** @var \Drupal\commerce_order\Adjustment $adjustment */
+    $adjustment = $object->getValue();
+    $attributes['type'] = $adjustment->getType();
+    $attributes['label'] = $adjustment->getLabel();
+    $attributes['amount'] = $adjustment->getAmount()->toArray();
+    $attributes['percentage'] = $adjustment->getPercentage();
+    $attributes['sourceId'] = $adjustment->getSourceId();
+    $attributes['included'] = $adjustment->isIncluded();
+    $attributes['locked'] = $adjustment->isLocked();
+    return $attributes;
+  }
+
+}