'Media bulk upload' on site server using 'Dropzonejs module' in Drupal 8 gives "failed to open the output stream" error - dropzone.js

Question

My website uses Drupal 8 and we are using Dropzonejs module for "media bulk upload" option. In my local environment, I'm able to bulk upload media without any problems. However, on server environment (having same configuration as local) when I try to bulk upload media, it throws "failed to open the output stream" error.
Any solutions/answers/suggestions are most welcome and much needed.
NOTE: Single item uploads work fine. Also during bulk upload, the error happens once the progress bar reaches 100%.
The defect screenshot is here

Answer 1

As of Drupal 8.6, we need a patch in the core for this functionality to work properly. For the fix, three files need to be changed as under:
drupal/core/includes/files.inc (Line 234)
/* #var \Drupal\Core\StreamWrapper\StreamWrapperInterface $wrapper */
if ($wrapper = \Drupal::service('stream_wrapper_manager')->getViaUri($uri)) {
return $wrapper->getExternalUrl();
}
return FALSE;
drupal/core/modules/locale/src/StreamWrapper/TranslationsStream.php (line 48 replace function)
public function getExternalUrl() {
return FALSE;
}
3.drupal/core/modules/locale/tests/src/Functional/LocaleImportFunctionalTest.php
(Add at line 365)
* Tests that imported PO files aren't break the UI provided by "views".
*
* #throws \Behat\Mink\Exception\ExpectationException
*
* #link https://www.drupal.org/project/drupal/issues/2449895
*/
public function testPoFileImportAndAccessibilityOfFilesOverviewViewsPage() {
$this->container
->get('module_installer')
->install(['system', 'user', 'file', 'views']);
// Create and log in a user that's able to upload/import translations
// and has an access to the overview of files in a system.
$this->drupalLogin($this->drupalCreateUser([
'access administration pages',
'access files overview',
'administer languages',
'translate interface',
]));
// Import a dummy PO file.
$this->importPoFile($this->getPoFile(), [
'langcode' => 'fr',
]);
// The problem this test cover is exposed in an exception that is thrown
// by the "\Drupal\locale\StreamWrapper\TranslationsStream" when "views"
// module provides a page of files overview. Refer to the issue to find
// more information.
$this->drupalGet('admin/content/files');
$this->assertSession()->statusCodeEquals(200);
}
(At line 373, overwrite the following function)
public function importPoFile($contents, array $options = []) {
$file_system = $this->container->get('file_system');
$file_path = $file_system->tempnam('temporary://', 'po_') . '.po';
file_put_contents($file_path, $contents);
$options['files[file]'] = $file_path;
$this->drupalPostForm('admin/config/regional/translate/import', $options,
t('Import'));
$file_system->unlink($file_path);
}