Big performance regression with 11.9

After upgrading to 11.9, our GitLab instance's performance seems to have fallen off a cliff.
No hardware changes on our part. Now, every page load is taking is taking ~10 seconds.
This is on an instance with quad-core CPU, 16GB RAM, SSD.

System information
System:         Ubuntu 18.04
Proxy:          no
Current User:   git
Using RVM:      no
Ruby Version:   2.5.3p105
Gem Version:    2.7.6
Bundler Version:1.16.6
Rake Version:   12.3.2
Redis Version:  3.2.12
Git Version:    2.18.1
Sidekiq Version:5.2.5
Go Version:     unknown

GitLab information
Version:        11.9.1-ee
Revision:       b50dc44da0c
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
DB Version:     9.6.11
URL:            https://git.company.com
HTTP Clone URL: https://git.company.com/some-group/some-project.git
SSH Clone URL:  git@git.company.com:some-group/some-project.git
Elasticsearch:  no
Geo:            no
Using LDAP:     no
Using Omniauth: yes
Omniauth Providers:


GitLab Shell
Version:        8.7.1
Repository storage paths:
  • default: /var/opt/gitlab/git-data/repositories GitLab Shell path: /opt/gitlab/embedded/service/gitlab-shell Git: /opt/gitlab/embedded/bin/git
---- 
Checking GitLab subtasks ...

Checking GitLab Shell ...


GitLab Shell: ... GitLab Shell version >= 8.7.1 ? ... OK (8.7.1)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK


Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful


Checking GitLab Shell ... Finished


Checking Gitaly ...


Gitaly: ... default ... OK


Checking Gitaly ... Finished


Checking Sidekiq ...


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


Checking Sidekiq ... Finished


Checking Incoming Email ...


Incoming Email: ... Reply by email is disabled in config/gitlab.yml


Checking Incoming Email ... Finished


Checking LDAP ...


LDAP: ... LDAP is disabled in config/gitlab.yml


Checking LDAP ... Finished


Checking GitLab App ...


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? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
4/8 ... yes
4/10 ... yes
4/12 ... yes
4/14 ... yes
4/18 ... yes
4/19 ... yes
4/20 ... yes
4/21 ... yes
4/22 ... yes
4/23 ... yes
4/24 ... yes
4/25 ... yes
4/26 ... yes
4/27 ... yes
4/28 ... yes
4/29 ... yes
4/30 ... yes
4/31 ... yes
4/32 ... yes
4/33 ... yes
4/34 ... yes
4/37 ... yes
4/38 ... yes
4/39 ... yes
4/40 ... yes
4/41 ... yes
4/42 ... yes
4/43 ... yes
4/44 ... yes
4/45 ... yes
4/46 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.5.3)
Git version >= 2.18.0 ? ... yes (2.18.1)
Git user has default SSH configuration? ... yes
Active users: ... 10
Elasticsearch version 5.6 - 6.x? ... skipped (elasticsearch is disabled)


Checking GitLab App ... Finished


Checking GitLab subtasks ... Finished

Any other info I can add to help fix this?