The issue is about page loading like the following ones:

  1. Front page
  2. Taxonomy pages (for instance, https://talash.by/taxonomy/term/33)
  3. Any view pages in edit mode /admin/structure/views/view/block_content
  4. Content list page /admin/content
  5. User list page /admin/people

I have a message "The website encountered an unexpected error. Please try again later."

Apache log shows:

Uncaught PHP Exception Drupal\Component\Plugin\Exception\PluginNotFoundException: "The "tag" plugin does not exist." at /var/www/site/public_html/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php line 52,

The issue happens even if I make a site copy (files and database) on the same physical server, but as different virtual server. Internal pages can be loaded (for example, https://talash.by/terms-of-use)

I am using Drupal 8.2.4 (standard) on Ubuntu 16.04, with PHP 7.0.8-0ubuntu0.16.04.3 (cli).

These are the non-core modules:

  • Media Colorbox (colorbox) Module Not installed 8.x-1.2

    • Other Backup and Migrate (backup_migrate) Module Not installed 8.x-4.0-alpha1

    • Other Colorbox Inline (colorbox_inline) Module Not installed 8.x-1.0-rc2

    • Other Disqus (disqus) Module Enabled 8.x-1.0-rc3

    • Other Exclude node title (exclude_node_title) Module Not installed 8.x-1.0-beta1+7-dev

    • Other Ultimate Cron (ultimate_cron) Module Not installed 8.x-2.0-alpha1

    • Web services HAL (hal)
      Bootstrap Bootstrap (bootstrap)

    • Theme Enabled 8.x-3.1
      Bootstrap Bootstrap Clean Blog (bootstrap_clean_blog)
    • Theme Enabled 8.x-1.0-rc2
  • Welcome to Drupal Answers! While it could be clear what you are saying, it's not clear what you are asking, since you aren't asking any explicit question. Stack Exchange doesn't work well with implicit questions. What don't you understand? What did you find about that error message? What don't you understand in the given explanation?
    – apaderno
    Jan 1, 2017 at 20:28
  • I have the same problem after our webserver switched from MySQL to MariaDB
    – 0711master
    Nov 11, 2022 at 10:14

1 Answer 1


Tag is the views cache plugin: \Drupal\views\Plugin\views\cache\Tag, that is in core.

If you are missing that then the files of your installation are messed up, you are possibly missing other files as well. You might want to re-upload all files and also consider using a more reliable deployment method like composer and not upload files over FTP or so.

  • Many thanks. You are right. The main problem was because of wrong configuration of a .gitignore file in the root folder. It had a string with a word "cache" and when I made a clone on the production server it does not download a folder itself and all files inside this "core/modules/views/src/Plugin/views/cache". The next step is to figure out how to keep integrity of the project with composer. Thanks!
    – rizoma
    Jan 2, 2017 at 7:52

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