Hello,
here is a support request originally posted on the gitlab bug tracker. It seems that it’s more appropriated to ask here for such help in our case.
So thank you in advance for your help. 
Summary
We are unable to fetch comments in a Merge Request (approx 86 comments).
When we try to load the page, it try to load the comments in the Activity pannel but nothing appens. After 60 sec the following message is displayed and the Activity section remain empty :
In the production.log file we can see the following error :
Completed 500 Internal Server Error in 60172ms (ActiveRecord: 245.1ms | Elasticsearch: 0.0ms | Allocations: 31442154)
Rack::Timeout::RequestTimeoutException (Request ran for longer than 60000ms ):
lib/feature.rb:249:in `block in current_feature_value'
lib/feature.rb:264:in `with_feature'
lib/feature.rb:245:in `current_feature_value'
lib/feature.rb:101:in `enabled?'
lib/gitlab/diff/highlight.rb:64:in `apply_marker_ranges_highlight'
lib/gitlab/diff/highlight.rb:35:in `block in highlight'
lib/gitlab/diff/highlight.rb:29:in `map'
lib/gitlab/diff/highlight.rb:29:in `with_index'
lib/gitlab/diff/highlight.rb:29:in `highlight'
lib/gitlab/diff/file.rb:203:in `highlighted_diff_lines'
lib/gitlab/discussions_diff/file_collection.rb:74:in `block in highlighted_lines_by_ids'
lib/gitlab/discussions_diff/file_collection.rb:73:in `transform_values'
lib/gitlab/discussions_diff/file_collection.rb:73:in `highlighted_lines_by_ids'
lib/gitlab/discussions_diff/file_collection.rb:35:in `load_highlight'
app/controllers/projects/merge_requests_controller.rb:319:in `discussions'
app/controllers/application_controller.rb:582:in `block in allow_gitaly_ref_name_caching'
lib/gitlab/gitaly_client.rb:324:in `allow_ref_name_caching'
app/controllers/application_controller.rb:581:in `allow_gitaly_ref_name_caching'
app/controllers/application_controller.rb:533:in `set_current_admin'
lib/gitlab/session.rb:11:in `with_session'
app/controllers/application_controller.rb:524:in `set_session_storage'
lib/gitlab/i18n.rb:107:in `with_locale'
lib/gitlab/i18n.rb:113:in `with_user_locale'
app/controllers/application_controller.rb:512:in `set_locale'
app/controllers/application_controller.rb:506:in `set_current_context'
lib/gitlab/middleware/memory_report.rb:13:in `call'
lib/gitlab/middleware/speedscope.rb:13:in `call'
lib/gitlab/database/load_balancing/rack_middleware.rb:23:in `call'
lib/gitlab/jira/middleware.rb:19:in `call'
lib/gitlab/middleware/go.rb:20:in `call'
lib/gitlab/etag_caching/middleware.rb:21:in `call'
lib/gitlab/middleware/query_analyzer.rb:11:in `block in call'
lib/gitlab/database/query_analyzer.rb:37:in `within'
lib/gitlab/middleware/query_analyzer.rb:11:in `call'
lib/gitlab/middleware/multipart.rb:173:in `call'
lib/gitlab/middleware/read_only/controller.rb:50:in `call'
lib/gitlab/middleware/read_only.rb:18:in `call'
lib/gitlab/middleware/same_site_cookies.rb:27:in `call'
lib/gitlab/middleware/handle_malformed_strings.rb:21:in `call'
lib/gitlab/middleware/basic_health_check.rb:25:in `call'
lib/gitlab/middleware/handle_ip_spoof_attack_error.rb:25:in `call'
lib/gitlab/middleware/request_context.rb:21:in `call'
lib/gitlab/middleware/webhook_recursion_detection.rb:15:in `call'
config/initializers/fix_local_cache_middleware.rb:11:in `call'
lib/gitlab/middleware/compressed_json.rb:37:in `call'
lib/gitlab/middleware/rack_multipart_tempfile_factory.rb:19:in `call'
lib/gitlab/middleware/sidekiq_web_static.rb:20:in `call'
lib/gitlab/metrics/requests_rack_middleware.rb:77:in `call'
lib/gitlab/middleware/release_env.rb:13:in `call'
Steps to reproduce
Reach a merge request with several comments then wait for the comments to load.
What is the current bug behavior?
After 60 sec the following message is displayed and the Activity section remain empty :
What is the expected correct behavior?
The comments should be loaded and readable.
Relevant logs and/or screenshots
See previous sections.
Results of GitLab environment info
gitlab-ce 15.7.5-ce.0
We tried to change the following parameters and reconfiguring gitlab, as we found some clues on others issues without any success :
puma[‘per_worker_max_memory_mb’] puma[‘worker_timeout’]
We doubled the values but the problem is still present.
Thank you