Alternate solution suggested by Bubasuma

Author: glo35082

app/code/Magento/ImportExport/Controller/Adminhtml/Import/Download.php

@@ -106,19 +106,13 @@ public function execute()
         $fileSize = $this->sampleFileProvider->getSize($entityName);
         $fileName = $entityName . '.csv';
 
-        $this->fileFactory->create(
+        return $this->fileFactory->create(
             $fileName,
-            null,
+            $fileContents,
             DirectoryList::VAR_IMPORT_EXPORT,
             'application/octet-stream',
             $fileSize
         );
-
-        $resultRaw = $this->resultRawFactory->create();
-        $resultRaw->setContents($fileContents)
-            ->setHeader('Content-Disposition', 'attachment; filename=' . $fileName);
-
-        return $resultRaw;
     }
 
     /**