Merging not possible after 12.1.4-ee upgrade

Summary

We upgraded from 12.0.0-ee.0 to 12.1.4-ee.0 through the Debian 9 repository yesterday and it is not possible to merge (even after approving them). Tested with old and new merge requests. I am owner of the project and protected branches are enabled for master, but Maintainer can merge. One or two hours after upgrading, the sidekick process was using 100% cpu and all queues were full (not sure if this is related or not)

Steps to reproduce

May be upgrade from 12.0 to 12.1.4(?)

Example Project

N/A

What is the current bug behavior?

Merging is not possible.

What is the expected correct behavior?

Merging should be possible.

Relevant logs and/or screenshots

nomerge_gitlab

Output of checks

Nothing in the logs.

Results of GitLab environment info

Expand for output related to GitLab environment info 
$ sudo gitlab-rake gitlab:env:info


System information
System:		Debian 9.9
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.6.3p62
Gem Version:	2.7.9
Bundler Version:1.17.3
Rake Version:	12.3.2
Redis Version:	3.2.12
Git Version:	2.21.0
Sidekiq Version:5.2.7
Go Version:	unknown


GitLab information
Version:	12.1.4-ee
Revision:	4ea82400e72
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	PostgreSQL
DB Version:	10.7
URL:		https://gitlab.company.io
HTTP Clone URL:	https://gitlab.company.io/some-group/some-project.git
SSH Clone URL:	git@gitlab.company.io:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers:


GitLab Shell
Version:	9.3.0
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 
$ sudo gitlab-rake gitlab:check SANITIZE=true
Checking GitLab subtasks ...


Checking GitLab Shell ...


GitLab Shell: ... GitLab Shell version >= 9.3.0 ? ... OK (9.3.0)
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: ...
5/8 ... yes
5/9 ... yes
5/10 ... yes
5/11 ... yes
8/12 ... yes
5/13 ... yes
8/14 ... yes
5/15 ... yes
9/17 ... yes
9/18 ... yes
20/19 ... yes
12/20 ... yes
5/21 ... yes
10/22 ... yes
8/23 ... yes
20/24 ... yes
14/25 ... yes
20/27 ... yes
6/28 ... yes
8/29 ... yes
17/30 ... yes
20/31 ... yes
17/32 ... yes
17/33 ... yes
20/34 ... yes
19/38 ... yes
20/41 ... yes
10/42 ... yes
10/43 ... yes
20/44 ... yes
20/45 ... yes
20/46 ... yes
20/47 ... yes
10/49 ... yes
10/50 ... yes
10/51 ... yes
10/52 ... yes
10/54 ... yes
10/55 ... yes
10/56 ... yes
10/57 ... yes
10/59 ... yes
10/60 ... yes
10/61 ... yes
10/63 ... yes
10/64 ... yes
17/65 ... yes
17/66 ... yes
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17/68 ... yes
10/69 ... yes
10/70 ... yes
23/71 ... yes
10/72 ... yes
10/74 ... yes
10/75 ... yes
10/76 ... yes
10/78 ... yes
10/79 ... yes
10/82 ... yes
10/84 ... yes
10/85 ... yes
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10/87 ... yes
27/88 ... yes
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27/91 ... yes
27/92 ... yes
27/93 ... yes
27/94 ... yes
6/95 ... yes
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10/101 ... yes
27/102 ... yes
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7/105 ... yes
27/106 ... yes
10/108 ... yes
23/109 ... yes
10/110 ... yes
10/111 ... yes
10/112 ... yes
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10/115 ... yes
32/116 ... yes
32/117 ... yes
27/118 ... yes
10/120 ... yes
33/122 ... yes
10/123 ... yes
32/124 ... yes
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20/127 ... yes
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33/132 ... yes
10/133 ... yes
34/134 ... yes
32/135 ... yes
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37/139 ... yes
37/140 ... yes
36/141 ... yes
32/142 ... yes
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36/144 ... yes
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32/148 ... yes
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36/151 ... yes
32/152 ... yes
10/153 ... yes
42/154 ... yes
42/155 ... yes
36/156 ... yes
32/157 ... yes
50/158 ... yes
10/159 ... yes
32/160 ... yes
53/162 ... yes
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54/167 ... yes
55/168 ... yes
56/169 ... yes
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56/174 ... yes
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32/195 ... yes
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36/197 ... yes
27/198 ... yes
27/200 ... yes
36/201 ... yes
68/202 ... yes
32/203 ... yes
68/204 ... yes
71/205 ... yes
68/206 ... yes
10/207 ... yes
73/208 ... yes
10/211 ... yes
37/212 ... yes
68/213 ... yes
27/214 ... yes
32/215 ... yes
68/217 ... yes
36/218 ... yes
36/219 ... yes
71/220 ... yes
71/221 ... yes
76/222 ... yes
81/223 ... yes
81/224 ... yes
32/225 ... yes
76/226 ... yes
81/227 ... yes
10/228 ... yes
81/229 ... yes
82/230 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.6.3)
Git version >= 2.21.0 ? ... yes (2.21.0)
Git user has default SSH configuration? ... yes
Active users: ... 25
Elasticsearch version 5.6 - 6.x? ... skipped (elasticsearch is disabled)


Checking GitLab App ... Finished


Checking GitLab subtasks ... Finished

Possible fixes

N/A

Any idea appreciated or if you need more information let me know.