Fixed race condition in deleting old adjustments

See #3901
Tested by customer here: https://app.frontapp.com/open/cnv_geujeix?key=nV4JNZkyEDPmMZxQ-f4Pwpev3ko5rULf

Author: lukeholder

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Release Notes for Craft Commerce
 
+## Unreleased
+
+- Fixed a PHP error that could occur when saving an Order. ([#3901](https://github.com/craftcms/commerce/pull/3901))
+
 ## 4.8.4 - 2025-05-01
 
 - Fixed a bug where products weren’t getting updated when default variants were saved directly. ([#3988](https://github.com/craftcms/commerce/issues/3988))

src/elements/Order.php

@@ -42,7 +42,6 @@
 use craft\commerce\Plugin;
 use craft\commerce\records\LineItem as LineItemRecord;
 use craft\commerce\records\Order as OrderRecord;
-use craft\commerce\records\OrderAdjustment as OrderAdjustmentRecord;
 use craft\commerce\records\OrderNotice as OrderNoticeRecord;
 use craft\commerce\records\Transaction as TransactionRecord;
 use craft\commerce\validators\StoreCountryValidator;
@@ -3402,11 +3401,6 @@ public function getMetadata(): array
      */
     private function _saveAdjustments(): void
     {
-        /** @var null|array|OrderAdjustmentRecord[] $previousAdjustments */
-        $previousAdjustments = OrderAdjustmentRecord::find()
-            ->where(['orderId' => $this->id])
-            ->all();
-
         $newAdjustmentIds = [];
 
         foreach ($this->getAdjustments() as $adjustment) {
@@ -3416,12 +3410,6 @@ private function _saveAdjustments(): void
             $adjustment->orderId = $this->id;
         }
 
-        foreach ($previousAdjustments as $previousAdjustment) {
-            if (!in_array($previousAdjustment->id, $newAdjustmentIds, false)) {
-                $previousAdjustment->delete();
-            }
-        }
-
         // Make sure all other adjustments have been cleaned up.
         Db::delete(
             Table::ORDERADJUSTMENTS,