Merge request hangs in `Merge in progress`

Summary

Onm some MRs, when clicking on Accept, "Merge in progress" message started spinning indefinitely.

Steps to reproduce

  1. Create a MR.
  2. Click on Accept.

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:		Debian 8.9
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.3.5p376
Gem Version:	2.6.13
Bundler Version:1.13.7
Rake Version:	12.0.0
Redis Version:	3.2.5
Git Version:	2.13.5
Sidekiq Version:5.0.4
Go Version:	unknown

GitLab information
Version:	10.0.3-ee
Revision:	eff7821
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
DB Version:	9.6.3
URL:		https://gitlab.stanley-robotics.xyz
HTTP Clone URL:	https://gitlab.stanley-robotics.xyz/some-group/some-project.git
SSH Clone URL:	git@gitlab-ssh.stanley-robotics.xyz:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: google_oauth2


GitLab Shell
Version:	5.9.0
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 >= 5.9.0 ? ... OK (5.9.0)
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: ...
3/22 ... ok
3/23 ... ok
3/24 ... ok
3/25 ... ok
3/26 ... ok
3/27 ... ok
3/28 ... ok
3/29 ... ok
3/30 ... ok
3/31 ... ok
24/32 ... ok
3/33 ... ok
3/34 ... ok
3/35 ... ok
3/36 ... ok
3/37 ... ok
3/38 ... ok
3/40 ... ok
3/41 ... ok
3/42 ... ok
3/43 ... ok
3/44 ... ok
3/45 ... ok
3/47 ... ok
4/48 ... ok
4/49 ... ok
18/50 ... ok
5/51 ... ok
4/52 ... ok
4/53 ... ok
3/54 ... ok
3/55 ... ok
10/56 ... ok
3/57 ... ok
4/58 ... ok
2/59 ... ok
17/60 ... ok
5/61 ... ok
17/62 ... ok
17/63 ... ok
17/64 ... ok
3/65 ... ok
17/67 ... ok
3/68 ... ok
5/69 ... ok
18/70 ... ok
3/71 ... ok
18/72 ... ok
3/73 ... ok
18/75 ... ok
3/77 ... ok
4/78 ... ok
3/79 ... ok
3/80 ... ok
17/81 ... ok
25/82 ... ok
25/84 ... ok
25/85 ... ok
25/86 ... ok
25/87 ... ok
25/88 ... ok
25/89 ... repository is empty
25/90 ... ok
25/91 ... ok
25/92 ... ok
25/93 ... ok
25/94 ... ok
25/95 ... ok
25/96 ... ok
25/97 ... ok
25/98 ... ok
25/99 ... ok
25/100 ... ok
25/101 ... ok
25/102 ... ok
25/103 ... ok
25/104 ... ok
25/105 ... ok
25/106 ... ok
25/107 ... ok
25/108 ... ok
25/109 ... ok
4/110 ... ok
17/111 ... ok
17/113 ... ok
3/114 ... ok
3/115 ... ok
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


Reply by email is disabled in config/gitlab.yml
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: ...
3/22 ... yes
3/23 ... yes
3/24 ... yes
3/25 ... yes
3/26 ... yes
3/27 ... yes
3/28 ... yes
3/29 ... yes
3/30 ... yes
3/31 ... yes
24/32 ... yes
3/33 ... yes
3/34 ... yes
3/35 ... yes
3/36 ... yes
3/37 ... yes
3/38 ... yes
3/40 ... yes
3/41 ... yes
3/42 ... yes
3/43 ... yes
3/44 ... yes
3/45 ... yes
3/47 ... yes
4/48 ... yes
4/49 ... yes
18/50 ... yes
5/51 ... yes
4/52 ... yes
4/53 ... yes
3/54 ... yes
3/55 ... yes
10/56 ... yes
3/57 ... yes
4/58 ... yes
2/59 ... yes
17/60 ... yes
5/61 ... yes
17/62 ... yes
17/63 ... yes
17/64 ... yes
3/65 ... yes
17/67 ... yes
3/68 ... yes
5/69 ... yes
18/70 ... yes
3/71 ... yes
18/72 ... yes
3/73 ... yes
18/75 ... yes
3/77 ... yes
4/78 ... yes
3/79 ... yes
3/80 ... yes
17/81 ... yes
25/82 ... yes
25/84 ... yes
25/85 ... yes
25/86 ... yes
25/87 ... yes
25/88 ... yes
25/89 ... yes
25/90 ... yes
25/91 ... yes
25/92 ... yes
25/93 ... yes
25/94 ... yes
25/95 ... yes
25/96 ... yes
25/97 ... yes
25/98 ... yes
25/99 ... yes
25/100 ... yes
25/101 ... yes
25/102 ... yes
25/103 ... yes
25/104 ... yes
25/105 ... yes
25/106 ... yes
25/107 ... yes
25/108 ... yes
25/109 ... yes
4/110 ... yes
17/111 ... yes
17/113 ... yes
3/114 ... yes
3/115 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.3 ? ... yes (2.3.5)
Git version >= 2.7.3 ? ... yes (2.13.5)
Git user has default SSH configuration? ... no
Try fixing it:
mkdir ~/gitlab-check-backup-1508438903
sudo mv /var/opt/gitlab/.ssh/id_rsa.pub ~/gitlab-check-backup-1508438903
sudo mv /var/opt/gitlab/.ssh/authorized_keys.lock ~/gitlab-check-backup-1508438903
sudo mv /var/opt/gitlab/.ssh/id_rsa ~/gitlab-check-backup-1508438903
For more information see:
doc/ssh/README.md in section "SSH on the GitLab server"
Please fix the error above and rerun the checks.
Active users: ... 16
Elasticsearch version 5.1 - 5.5? ... skipped (elasticsearch is disabled)


Checking GitLab ... Finished