Encounter Time out Error at some page after Upgrade

How to Use GitLab Upgrade
1

I had upgraded gitlab to 10.8.7 from 9.5.10.
After upgrade, encounter 500 error at some pages.
Error log is below.
I checked sidekiq, but background migration was finished.
After a while, I reload the page and it was displayed normally.
Is this due to migration? If so, how do I know if the migration is complete?

Thanks.

Completed 500 Internal Server Error in 15106ms (ActiveRecord: 4.1ms)

Timeout::Error (Timeout waiting for process #24846):
  lib/gitlab/git/popen.rb:94:in `process_wait_with_timeout'
  lib/gitlab/git/popen.rb:60:in `popen_with_timeout'
  lib/gitlab/git/repository.rb:1691:in `block in run_git_with_timeout'
  lib/gitlab/git/storage/circuit_breaker.rb:41:in `perform'
  lib/gitlab/git/repository.rb:1690:in `run_git_with_timeout'
  lib/gitlab/git/repository.rb:2509:in `last_commit_id_for_path_by_shelling_out'
  lib/gitlab/git/repository.rb:1995:in `last_commit_for_path_by_rugged'
  lib/gitlab/git/repository.rb:1540:in `block in last_commit_for_path'
  lib/gitlab/gitaly_client.rb:268:in `block (2 levels) in migrate'
  lib/gitlab/gitaly_client.rb:312:in `allow_n_plus_1_calls'
  lib/gitlab/gitaly_client.rb:261:in `block in migrate'
  lib/gitlab/metrics/influx_db.rb:98:in `measure'
  lib/gitlab/gitaly_client.rb:259:in `migrate'
  lib/gitlab/git/repository.rb:1448:in `gitaly_migrate'
  lib/gitlab/git/repository.rb:1536:in `last_commit_for_path'
  app/models/repository.rb:632:in `last_commit_for_path'
  app/controllers/projects/refs_controller.rb:58:in `block (2 levels) in logs_tree'
  app/controllers/projects/refs_controller.rb:56:in `map'
  app/controllers/projects/refs_controller.rb:56:in `block in logs_tree'
  lib/gitlab/gitaly_client.rb:312:in `allow_n_plus_1_calls'
  app/controllers/projects/refs_controller.rb:55:in `logs_tree'
  lib/gitlab/i18n.rb:50:in `with_locale'
  lib/gitlab/i18n.rb:56:in `with_user_locale'
  app/controllers/application_controller.rb:355:in `set_locale'
  lib/gitlab/middleware/multipart.rb:95: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:28:in `call'
  lib/gitlab/middleware/read_only.rb:16: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'