milestones.json and labels.json return html page instead of JSON

Summary

We noticed today that our gitlab instance upgraded to 10.3.2 no longer allows us to select milestones or labels from the issue page. The milestone dropdown is empty and says "No Milestone" and if we click Edit for Labels there is a search box with "undefined" appearing underneath.

Steps to reproduce

1. Open any issue
2. Click on Edit beside Milestone or Labels

Example Project

This is on our own self-hosted gitlab.

What is the current bug behavior?

No milestones appear, and under labels it says undefined.

What is the expected correct behavior?

I should see a list of milestones, or labels.

Relevant logs and/or screenshots

If I open the Chrome developer tools and look at the network requests, the requests it's making to /some-group/some-project/milestones.json is return a HTML page response instead of a JSON object. Same with the labels request.

I can attach a screenshot if it helps. Here is a log of a milestone request.

Request URL:https://git.example.com/groupName/projectName/milestones.json
Request Method:GET

Response Headers:
cache-control:max-age=0, private, must-revalidate
content-type:text/html; charset=utf-8
date:Tue, 02 Jan 2018 16:29:01 GMT
etag:W/"16c9b94ef0b4cfb843c85d494b73de28"
server:nginx
status:200
strict-transport-security:max-age=31536000
x-content-type-options:nosniff
x-frame-options:DENY
x-request-id:bab71337-86ef-4035-838b-00fb3f2d204f
x-runtime:0.099707
x-ua-compatible:IE=edge
x-xss-protection:1; mode=block

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:		Debian 8.10
Current User:	git
Using RVM:	no
Ruby Version:	2.3.5p376
Gem Version:	2.6.13
Bundler Version:1.13.7
Rake Version:	12.3.0
Redis Version:	3.2.11
Git Version:	2.14.3
Sidekiq Version:5.0.4
Go Version:	go1.7.4 linux/amd64
GitLab information
Version:	10.3.2
Revision:	5fbc5f2
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
URL:		https://git.nerdsonsite.com
HTTP Clone URL:	https://git.nerdsonsite.com/some-group/some-project.git
SSH Clone URL:	git@git.nerdsonsite.com:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: google_oauth2
GitLab Shell
Version:	5.10.2
Repository storage paths:

• default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab Shell ...
GitLab Shell version >= 5.10.2 ? ... OK (5.10.2)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
4/2 ... ok
4/5 ... ok
4/6 ... ok
4/7 ... ok
4/8 ... ok
4/9 ... ok
4/11 ... ok
4/14 ... ok
4/17 ... ok
13/18 ... ok
13/19 ... ok
13/20 ... ok
13/21 ... ok
13/22 ... ok
13/23 ... ok
13/24 ... ok
13/25 ... ok
13/26 ... ok
13/27 ... ok
13/28 ... ok
13/29 ... ok
13/30 ... ok
13/31 ... ok
13/32 ... repository is empty
13/33 ... ok
13/34 ... ok
13/35 ... repository is empty
13/36 ... ok
13/37 ... ok
13/38 ... ok
13/39 ... ok
13/40 ... ok
13/41 ... ok
13/42 ... ok
18/43 ... ok
18/44 ... ok
3/45 ... ok
20/46 ... repository is empty
9/47 ... ok
4/48 ... ok
9/49 ... ok
3/50 ... ok
4/51 ... ok
9/52 ... ok
9/53 ... ok
9/54 ... ok
9/55 ... ok
9/56 ... ok
9/57 ... ok
11/58 ... ok
15/59 ... ok
26/60 ... repository is empty
9/61 ... ok
9/62 ... ok
13/63 ... ok
9/64 ... ok
9/66 ... ok
3/67 ... ok
9/68 ... ok
4/69 ... ok
9/70 ... ok
3/71 ... ok
3/72 ... ok
34/73 ... ok
34/74 ... ok
9/75 ... repository is empty
9/76 ... ok
3/77 ... ok
13/78 ... ok
38/79 ... ok
13/80 ... ok
4/81 ... ok
9/84 ... ok
9/85 ... ok
9/86 ... ok
9/87 ... ok
9/88 ... ok
9/89 ... ok
9/90 ... ok
9/91 ... ok
9/92 ... ok
9/93 ... ok
9/94 ... ok
9/95 ... ok
9/96 ... ok
9/97 ... ok
9/98 ... ok
9/99 ... ok
9/100 ... ok
9/101 ... ok
9/102 ... ok
9/103 ... ok
9/104 ... ok
9/105 ... ok
9/106 ... ok
9/107 ... ok
9/108 ... ok
9/109 ... ok
9/110 ... ok
9/111 ... ok
3/112 ... repository is empty
4/113 ... ok
9/114 ... ok
9/115 ... ok
9/116 ... ok
9/117 ... ok
9/118 ... ok
9/119 ... ok
9/120 ... ok
9/121 ... ok
9/122 ... ok
9/123 ... ok
9/124 ... ok
9/125 ... ok
9/126 ... repository is empty
9/127 ... ok
9/128 ... ok
9/129 ... ok
9/130 ... ok
9/131 ... ok
9/132 ... ok
9/133 ... ok
9/134 ... ok
9/135 ... ok
9/136 ... ok
9/137 ... ok
9/138 ... ok
9/139 ... ok
9/140 ... ok
9/141 ... ok
9/142 ... ok
9/143 ... ok
9/144 ... ok
9/145 ... ok
9/146 ... ok
13/147 ... ok
4/148 ... ok
4/150 ... ok
9/151 ... ok
9/153 ... ok
9/154 ... ok
9/155 ... ok
38/157 ... ok
38/158 ... ok
15/159 ... ok
4/160 ... ok
4/161 ... repository is empty
4/163 ... ok
4/164 ... ok
4/165 ... ok
3/167 ... ok
9/168 ... ok
4/169 ... ok
4/170 ... ok
3/171 ... repository is empty
9/172 ... ok
4/173 ... ok
9/174 ... ok
4/175 ... ok
9/176 ... ok
4/177 ... ok
4/178 ... repository is empty
4/179 ... ok
4/180 ... repository is empty
3/181 ... ok
4/182 ... repository is empty
4/183 ... repository is empty
13/184 ... ok
4/185 ... ok
56/186 ... ok
56/187 ... ok
4/188 ... ok
4/189 ... repository is empty
4/190 ... repository is empty
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 Sidekiq ...
Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Checking Reply by email ...
IMAP server credentials are correct? ... yes
Init.d configured correctly? ... skipped
MailRoom running? ... skipped
Checking Reply by email ... Finished
Checking LDAP ...
LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab ...
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: ...
4/2 ... yes
4/5 ... yes
4/6 ... yes
4/7 ... yes
4/8 ... yes
4/9 ... yes
4/11 ... yes
4/14 ... yes
4/17 ... yes
13/18 ... yes
13/19 ... yes
13/20 ... yes
13/21 ... yes
13/22 ... yes
13/23 ... yes
13/24 ... yes
13/25 ... yes
13/26 ... yes
13/27 ... yes
13/28 ... yes
13/29 ... yes
13/30 ... yes
13/31 ... yes
13/32 ... yes
13/33 ... yes
13/34 ... yes
13/35 ... yes
13/36 ... yes
13/37 ... yes
13/38 ... yes
13/39 ... yes
13/40 ... yes
13/41 ... yes
13/42 ... yes
18/43 ... yes
18/44 ... yes
3/45 ... yes
20/46 ... yes
9/47 ... yes
4/48 ... yes
9/49 ... yes
3/50 ... yes
4/51 ... yes
9/52 ... yes
9/53 ... yes
9/54 ... yes
9/55 ... yes
9/56 ... yes
9/57 ... yes
11/58 ... yes
15/59 ... yes
26/60 ... yes
9/61 ... yes
9/62 ... yes
13/63 ... yes
9/64 ... yes
9/66 ... yes
3/67 ... yes
9/68 ... yes
4/69 ... yes
9/70 ... yes
3/71 ... yes
3/72 ... yes
34/73 ... yes
34/74 ... yes
9/75 ... yes
9/76 ... yes
3/77 ... yes
13/78 ... yes
38/79 ... yes
13/80 ... yes
4/81 ... yes
9/84 ... yes
9/85 ... yes
9/86 ... yes
9/87 ... yes
9/88 ... yes
9/89 ... yes
9/90 ... yes
9/91 ... yes
9/92 ... yes
9/93 ... yes
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9/95 ... yes
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9/99 ... yes
9/100 ... yes
9/101 ... yes
9/102 ... yes
9/103 ... yes
9/104 ... yes
9/105 ... yes
9/106 ... yes
9/107 ... yes
9/108 ... yes
9/109 ... yes
9/110 ... yes
9/111 ... yes
3/112 ... yes
4/113 ... yes
9/114 ... yes
9/115 ... yes
9/116 ... yes
9/117 ... yes
9/118 ... yes
9/119 ... yes
9/120 ... yes
9/121 ... yes
9/122 ... yes
9/123 ... yes
9/124 ... yes
9/125 ... yes
9/126 ... yes
9/127 ... yes
9/128 ... yes
9/129 ... yes
9/130 ... yes
9/131 ... yes
9/132 ... yes
9/133 ... yes
9/134 ... yes
9/135 ... yes
9/136 ... yes
9/137 ... yes
9/138 ... yes
9/139 ... yes
9/140 ... yes
9/141 ... yes
9/142 ... yes
9/143 ... yes
9/144 ... yes
9/145 ... yes
9/146 ... yes
13/147 ... yes
4/148 ... yes
4/150 ... yes
9/151 ... yes
9/153 ... yes
9/154 ... yes
9/155 ... yes
38/157 ... yes
38/158 ... yes
15/159 ... yes
4/160 ... yes
4/161 ... yes
4/163 ... yes
4/164 ... yes
4/165 ... yes
3/167 ... yes
9/168 ... yes
4/169 ... yes
4/170 ... yes
3/171 ... yes
9/172 ... yes
4/173 ... yes
9/174 ... yes
4/175 ... yes
9/176 ... yes
4/177 ... yes
4/178 ... yes
4/179 ... yes
4/180 ... yes
3/181 ... yes
4/182 ... yes
4/183 ... yes
13/184 ... yes
4/185 ... yes
56/186 ... yes
56/187 ... yes
4/188 ... yes
4/189 ... yes
4/190 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.3.5)
Git version >= 2.7.3 ? ... yes (2.14.3)
Git user has default SSH configuration? ... yes
Active users: ... 27
Checking GitLab ... Finished

Possible fixes

Have not been able to find any possible fixes.