MAGETWO-75935: Search results is not the same for the same search queries

Author: AVoskoboinikov

app/code/Magento/CatalogSearch/Model/ResourceModel/Fulltext/Collection.php

@@ -61,7 +61,7 @@ class Collection extends \Magento\Catalog\Model\ResourceModel\Product\Collection
     /**
      * @var string|null
      */
-    private $order = null;
+    private $relevanceOrderDirection = null;
 
     /**
      * @var string
@@ -361,13 +361,16 @@ protected function _renderFiltersBefore()
             []
         );
 
-        if ($this->order && 'relevance' === $this->order['field']) {
-            $this->getSelect()->order('search_result.'. TemporaryStorage::FIELD_SCORE . ' ' . $this->order['dir']);
+        if ($this->relevanceOrderDirection) {
+            $this->getSelect()->order(
+                'search_result.'. TemporaryStorage::FIELD_SCORE . ' ' . $this->relevanceOrderDirection
+            );
         }
 
         /*
          * This order is required to force search results be the same
          * for the same requests and products with the same relevance
+         * NOTE: this does not replace existing orders but ADDs one more
          */
         $this->setOrder('entity_id');
 
@@ -392,10 +395,12 @@ protected function _renderFilters()
      */
     public function setOrder($attribute, $dir = Select::SQL_DESC)
     {
-        $this->order = ['field' => $attribute, 'dir' => $dir];
-        if ($attribute !== 'relevance') {
+        if ($attribute === 'relevance') {
+            $this->relevanceOrderDirection = $dir;
+        } else {
             parent::setOrder($attribute, $dir);
         }
+
         return $this;
     }