Sidekiq RuntimeError: Circular dependency detected

Zendesk issue: https://gitlab.zendesk.com/agent/tickets/17933

System information
System:		Ubuntu 14.04
Current User:	git
Using RVM:	no
Ruby Version:	2.1.6p336
Gem Version:	2.2.3
Bundler Version:1.9.9
Rake Version:	10.5.0
Sidekiq Version:4.0.1

GitLab information
Version:	8.4.4
Revision:	9c31cc6
Directory:	/home/git/gitlab
DB Adapter:	mysql2
URL:		https://xxx
HTTP Clone URL:	https://xxx/some-group/some-project.git
SSH Clone URL:	git@xxx:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: github

GitLab Shell
Version:	2.6.10
Repositories:	/home/git/repositories/
Hooks:		/home/git/gitlab-shell/hooks/
Git:		/usr/bin/git

2016-02-17T09:46:21.033Z 10004 TID-ovl6bih48 WARN: RuntimeError: Circular dependency detected while autoloading constant Banzai::Pipeline::ReferenceExtractionPipeline
2016-02-17T09:46:21.033Z 10004 TID-ovl6bih48 WARN: /home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/dependencies.rb:492:in `load_missing_constant'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/activesupport-4.2.5.1/lib/active_support/dependencies.rb:184:in `const_missing'
/home/git/gitlab/lib/banzai/pipeline.rb:5:in `const_get'
/home/git/gitlab/lib/banzai/pipeline.rb:5:in `[]'
/home/git/gitlab/lib/banzai/renderer.rb:31:in `render_result'
/home/git/gitlab/lib/banzai/reference_extractor.rb:47:in `block (2 levels) in references'
/home/git/gitlab/lib/banzai/reference_extractor.rb:45:in `each'
/home/git/gitlab/lib/banzai/reference_extractor.rb:45:in `flat_map'
/home/git/gitlab/lib/banzai/reference_extractor.rb:45:in `block in references'
/home/git/gitlab/lib/banzai/reference_extractor.rb:17:in `call'
/home/git/gitlab/lib/banzai/reference_extractor.rb:17:in `lazily'
/home/git/gitlab/lib/banzai/reference_extractor.rb:44:in `references'
/home/git/gitlab/lib/gitlab/reference_extractor.rb:30:in `issues'
/home/git/gitlab/app/models/concerns/mentionable.rb:72:in `referenced_mentionables'
/home/git/gitlab/app/models/concerns/mentionable.rb:82:in `create_cross_references!'
/home/git/gitlab/app/services/git_push_service.rb:98:in `block in process_commit_messages'
/home/git/gitlab/app/services/git_push_service.rb:82:in `each'
/home/git/gitlab/app/services/git_push_service.rb:82:in `process_commit_messages'
/home/git/gitlab/app/services/git_push_service.rb:47:in `execute'
/home/git/gitlab/app/workers/post_receive.rb:41:in `block in perform'
/home/git/gitlab/app/workers/post_receive.rb:28:in `each'
/home/git/gitlab/app/workers/post_receive.rb:28:in `perform'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:150:in `execute_job'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:132:in `block (2 levels) in process'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:127:in `block in invoke'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/server/active_record.rb:6:in `call'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:129:in `block in invoke'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/server/retry_jobs.rb:74:in `call'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:129:in `block in invoke'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/server/logging.rb:11:in `block in call'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/logging.rb:30:in `with_context'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/server/logging.rb:7:in `call'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:129:in `block in invoke'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:132:in `call'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/middleware/chain.rb:132:in `invoke'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:127:in `block in process'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:166:in `stats'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:126:in `process'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:79:in `process_one'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/processor.rb:67:in `run'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/util.rb:16:in `watchdog'
/home/git/gitlab/vendor/bundle/ruby/2.1.0/gems/sidekiq-4.0.1/lib/sidekiq/util.rb:24:in `block in safe_thread'