server error 500 when trying to open Help page

Each time I'm trying to open the help page in the Gitlab CE 11.2.3 I got server error.

production log:

Started GET "/help" for 127.0.0.1 at 2018-09-11 16:27:15 +0500
Processing by HelpController#index as HTML
Started POST "/api/v4/jobs/request" for 127.0.0.1 at 2018-09-11 16:27:15 +0500
Completed 500 Internal Server Error in 153ms (ActiveRecord: 1.8ms)

ActionView::Template::Error (undefined method `add_class' for #<Nokogiri::XML::Element:0x0000000835810f00>):
    31: .row.prepend-top-default
    32:   .col-md-8
    33:     .documentation-index.wiki
    34:       = markdown(@help_index)
    35:   .col-md-4
    36:     .card
    37:       .card-header
  lib/banzai/filter/image_lazy_load_filter.rb:10:in `block in call'
  lib/banzai/filter/image_lazy_load_filter.rb:9:in `call'
  lib/banzai/pipeline/base_pipeline.rb:21:in `block (2 levels) in singleton class'
  lib/banzai/renderer.rb:108:in `render_result'
  lib/banzai/renderer.rb:139:in `block in cacheless_render'
  lib/gitlab/metrics/influx_db.rb:98:in `measure'
  lib/banzai/renderer.rb:138:in `cacheless_render'
  lib/banzai/renderer.rb:28:in `render'
  lib/banzai.rb:3:in `render'
  app/helpers/markup_helper.rb:246:in `markdown_unsafe'
  app/helpers/markup_helper.rb:91:in `markdown'
  app/views/help/index.html.haml:34:in `_app_views_help_index_html_haml__3710500830282665884_17630413960'
  lib/gitlab/i18n.rb:51:in `with_locale'
  lib/gitlab/i18n.rb:57:in `with_user_locale'
  app/controllers/application_controller.rb:401:in `set_locale'
  lib/gitlab/middleware/multipart.rb:97:in `call'
  lib/gitlab/request_profiler/middleware.rb:14:in `call'
  lib/gitlab/middleware/go.rb:17:in `call'
  lib/gitlab/etag_caching/middleware.rb:11:in `call'
  lib/gitlab/middleware/read_only/controller.rb:38:in `call'
  lib/gitlab/middleware/read_only.rb:16:in `call'
  lib/gitlab/middleware/basic_health_check.rb:25:in `call'
  lib/gitlab/request_context.rb:18:in `call'
  lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
  lib/gitlab/middleware/release_env.rb:10:in `call'

Results of GitLab environment info

Expand for output related to GitLab environment info

$ bundle exec rake gitlab:env:info RAILS_ENV=production

System information System: Current User: git Using RVM: no Ruby Version: 2.4.4p296 Gem Version: 2.7.7 Bundler Version:1.16.4 Rake Version: 12.3.1 Redis Version: 4.0.11 Git Version: 2.18.0 Sidekiq Version:5.2.1 Go Version: go1.11 freebsd/amd64

GitLab information Version: 11.2.3 Revision: Unknown Directory: /usr/local/www/gitlab-ce DB Adapter: mysql2 URL: http://XXXXXXXXXXXXXXX.net HTTP Clone URL: http://XXXXXXXXXXXXXXX.net/some-group/some-project.git SSH Clone URL: git@XXXXXXXXXXXXXXX.net:some-group/some-project.git Using LDAP: yes Using Omniauth: no

GitLab Shell Version: 8.1.1 Repository storage paths:

default: /usr/home/git/repositories Hooks: /usr/local/share/gitlab-shell/hooks Git: /usr/local/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

$ bundle exec rake gitlab:check RAILS_ENV=production Checking GitLab Shell ...

GitLab Shell version >= 8.1.1 ? ... OK (8.1.1) Repo base directory exists? default... yes Repo storage directories are symlinks? default... no Repo paths owned by git:root, or git:git? default... yes Repo paths access is drwxrws---? default... yes hooks directories in repos are links: ...

[... repositories are ok with two empty ones, I'm afraid I cannot disclose this info 'cause I'm under NDA ...]

Running /usr/local/share/gitlab-shell/bin/check Check GitLab API access: OK Redis available via internal API: OK

Access to /usr/home/git/.ssh/authorized_keys: OK gitlab-shell self-check successful

Checking GitLab Shell ... Finished

Checking Sidekiq ...

Running? ... yes Number of Sidekiq processes ... 1

Checking Sidekiq ... Finished

Reply by email is disabled in config/gitlab.yml Checking LDAP ...

Server: ldapmain LDAP authentication... Success LDAP users with access to your GitLab server (only showing the first 100 results) DN: cn=ХХХ,ou=users,dc=XXXX,dc=XXXX uid: XXX [... same story with LDAP usernames and CNs ...]

Checking LDAP ... Finished

Checking GitLab ...

Git configured correctly? ... yes Database config exists? ... yes All migrations up? ... yes Database contains orphaned GroupMembers? ... no GitLab config exists? ... yes GitLab config up to date? ... yes Log directory writable? ... yes Tmp directory writable? ... yes Uploads directory exists? ... yes Uploads directory has correct permissions? ... yes Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet) Init script exists? ... no Try fixing it: Install the init script For more information see: doc/install/installation.md in section "Install Init Script" Please fix the error above and rerun the checks. Init script up-to-date? ... can't check because of previous errors Projects have namespace: ...

[... namespaces check also went okay ...]

Redis version >= 2.8.0? ... yes Ruby version >= 2.3.5 ? ... yes (2.4.4) Git version >= 2.9.5 ? ... yes (2.18.0) Git user has default SSH configuration? ... no Try fixing it: mkdir ~/gitlab-check-backup-1536660944 sudo mv /usr/local/git/.ssh/dev_id_dsa ~/gitlab-check-backup-1536660944 sudo mv /usr/local/git/.ssh/id_dsa ~/gitlab-check-backup-1536660944 sudo mv /usr/local/git/.ssh/authorized_keys~ ~/gitlab-check-backup-1536660944 sudo mv /usr/local/git/.ssh/id_dsa.pub ~/gitlab-check-backup-1536660944 sudo mv /usr/local/git/.ssh/svn_id_dsa ~/gitlab-check-backup-1536660944 sudo mv /usr/local/git/.ssh/known_hosts.old ~/gitlab-check-backup-1536660944 For more information see: doc/ssh/README.md in section "SSH on the GitLab server" Please fix the error above and rerun the checks. Active users: ... 160

Checking GitLab ... Finished