Branches with "+" in the name do not display on GitLab

Summary

We upgraded our GitLab from 12.9.3 to 12.10.1 and since doing so, we cannot view branches/tags with "+" in the name on the GitLab website.

Steps to reproduce

1. Create or navigate to a branch containing a "+" in the name (i.e. Informal_5.00.20+).
2. View the tag/branch (i.e. https://[sanitized]/[group]/[project]/-/tree/Informal_5.00.20+)

Example Project

N/A; happening in an omnibus installation.

What is the current bug behavior?

The page loads but no files are shown; only the latest commit at the top of the files list appears; the rest of the page is empty.

What is the expected correct behavior?

The page loads and shows all files in the root of the branch, in addition to the latest commit at the top.

Relevant logs and/or screenshots

N/A

Output of checks

(If you are reporting a bug on GitLab.com, write: This bug happens on GitLab.com)

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:         RedHatEnterpriseServer 7.7
Current User:   git
Using RVM:      no
Ruby Version:   2.6.5p114
Gem Version:    2.7.10
Bundler Version:1.17.3
Rake Version:   12.3.3
Redis Version:  5.0.7
Git Version:    2.26.2
Sidekiq Version:5.2.7
Go Version:     unknown

GitLab information
Version:        12.10.1
Revision:       e658772bd63
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     PostgreSQL
DB Version:     11.7
URL:            https://[sanitized]
HTTP Clone URL: https://[sanitized]/some-group/some-project.git
SSH Clone URL:  git@[sanitized]:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: yes
Omniauth Providers:

GitLab Shell
Version:        12.2.0
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

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab subtasks ...
Checking GitLab Shell ...
GitLab Shell: ... GitLab Shell version >= 12.2.0 ? ... OK (12.2.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Internal API available: OK
Redis available via internal API: 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: ... Server: ldapmain
LDAP authentication... Success
LDAP users with access to your GitLab server (only showing the first 100 results)
User output sanitized. Found 100 users of 100 limit.
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: ...
2/1 ... yes
2/2 ... yes
2/3 ... yes
2/6 ... yes
17/8 ... yes
20/11 ... yes
17/13 ... yes
2/14 ... yes
2/15 ... yes
20/16 ... yes
2/17 ... yes
21/18 ... yes
2/22 ... yes
5/23 ... yes
20/24 ... yes
6/25 ... yes
2/26 ... yes
2/27 ... yes
4/28 ... yes
4/29 ... yes
2/30 ... yes
2/31 ... yes
10/32 ... yes
2/33 ... yes
21/34 ... yes
2/35 ... yes
15/36 ... yes
4/38 ... yes
2/39 ... yes
2/40 ... yes
2/41 ... yes
2/42 ... yes
2/43 ... yes
2/44 ... yes
2/45 ... yes
2/46 ... yes
14/47 ... yes
2/49 ... yes
2/50 ... yes
2/51 ... yes
2/52 ... yes
2/54 ... yes
2/57 ... yes
2/58 ... yes
6/59 ... yes
2/60 ... yes
2/61 ... yes
2/62 ... yes
2/66 ... yes
2/67 ... yes
2/68 ... yes
2/70 ... yes
11/71 ... yes
2/72 ... yes
26/74 ... yes
50/75 ... yes
4/76 ... yes
2/77 ... yes
2/79 ... yes
41/80 ... yes
4/81 ... yes
41/82 ... yes
2/83 ... yes
41/84 ... yes
41/87 ... yes
41/88 ... yes
74/89 ... yes
2/90 ... yes
2/91 ... yes
2/93 ... yes
57/94 ... yes
2/95 ... yes
2/97 ... yes
2/98 ... yes
82/99 ... yes
101/100 ... yes
Redis version >= 4.0.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.6.5)
Git version >= 2.22.0 ? ... yes (2.26.2)
Git user has default SSH configuration? ... yes
Active users: ... 80
Is authorized keys file accessible? ... yes
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished

Possible fixes

N/A