Gitlab: pushes registering with repo, but pipelines not running and projects dashbaord 'last updated' is not changed - gitlab

Question

When we push to our repository, we expect a pipeline to run. However, the pipelines have stopped starting automatically when we push.
In addition, when we try to start the pipeline manually, not all the tags and branches are showing in the dropdown list of tags and branches to choose from. When we browse the repository in Gitlab, we can see the branches and the pushed commits.
Finally, in the /dashboard/projects page, the 'last updated' date of the project is out of date, saying "yesterday" rather than "10 mins ago" (which is what shows when viewing the repository within the project.
We recently migrated server and so would expect that there is some migration issue going on here. Does anyone have any ideas where to look to solve this problem (i.e. what sub-systems could be not working/configured correctly to produce this behaviour)?
Gitlab version: 9.4.2
Run with Docker using: https://hub.docker.com/r/gitlab/gitlab-ce/
Update
I tailed the logs while pushing to the repository, what follows is a chunk of logs around that time (starting with the SSH connection for the push). Potentially the 404 around prometheus is interesting, but I'm not sure that's unexpected (we're not using it):
==> /var/log/gitlab/sshd/current <==
2017-08-01_17:05:16.86559 Accepted publickey for git from (removed) port 57680 ssh2: RSA SHA256:(removed)
==> /var/log/gitlab/gitlab-rails/production.log <==
Started POST "/api/v4/internal/allowed" for 127.0.0.1 at 2017-08-01 17:05:17 +0000
==> /var/log/gitlab/gitlab-shell/gitlab-shell.log <==
I, [2017-08-01T17:05:17.088866 #2286] INFO -- : POST http://127.0.0.1:8080/api/v4/internal/allowed 0.01170
I, [2017-08-01T17:05:17.089030 #2286] INFO -- : gitlab-shell: executing git command <git-receive-pack /var/opt/gitlab/git-data/repositories/products/preside-ext-ems.git> for user with key key-2.
==> /var/log/gitlab/sshd/current <==
2017-08-01_17:05:17.20480 Received disconnect from x.x.x.x port 57680:11: disconnected by user
2017-08-01_17:05:17.20483 Disconnected from x.x.x.x port 57680
==> /var/log/gitlab/gitlab-rails/production.log <==
Started GET "/-/metrics" for 127.0.0.1 at 2017-08-01 17:05:18 +0000
Processing by MetricsController#index as HTML
Filter chain halted as :validate_prometheus_metrics rendered or redirected
Completed 404 Not Found in 1ms (Views: 0.4ms | ActiveRecord: 0.0ms)
Started POST "/api/v4/jobs/request" for 172.17.0.1 at 2017-08-01 17:05:18 +0000
==> /var/log/gitlab/gitlab-workhorse/current <==
2017-08-01_17:05:18.16504 gitlab.mycompany.com # - - [2017-08-01 17:05:18.158505651 +0000 UTC] "POST /api/v4/jobs/request HTTP/1.1" 204 0 "" "gitlab-ci-multi-runner 9.4.1 (9-4-stable; go1.8.3; linux/amd64)" 0.006484
==> /var/log/gitlab/nginx/gitlab_access.log <==
172.17.0.1 - - [01/Aug/2017:17:05:18 +0000] "POST /api/v4/jobs/request HTTP/1.1" 204 0 "-" "gitlab-ci-multi-runner 9.4.1 (9-4-stable; go1.8.3; linux/amd64)"
==> /var/log/gitlab/gitlab-rails/production.log <==
Started POST "/api/v4/jobs/request" for 172.17.0.1 at 2017-08-01 17:05:23 +0000
==> /var/log/gitlab/gitlab-workhorse/current <==
2017-08-01_17:05:23.16534 gitlab.mycompany.com # - - [2017-08-01 17:05:23.159064793 +0000 UTC] "POST /api/v4/jobs/request HTTP/1.1" 204 0 "" "gitlab-ci-multi-runner 9.4.1 (9-4-stable; go1.8.3; linux/amd64)" 0.006235
==> /var/log/gitlab/nginx/gitlab_access.log <==
172.17.0.1 - - [01/Aug/2017:17:05:23 +0000] "POST /api/v4/jobs/request HTTP/1.1" 204 0 "-" "gitlab-ci-multi-runner 9.4.1 (9-4-stable; go1.8.3; linux/amd64)"

Answer 1

Not exactly an answer - but I have wiped out the server and rebuilt from scratch. Manually recreating each project and importing the repositories for each project.
A royal PITA, but everything is working as expected.
I can only guess that either something was setup on the host server that was causing issues (I did a clean install on the host to start again), or that there was something about simply copying over all our configuration and data dirs from the old server to the new server that caused issues (seems unlikely).
Not much help I'm afraid :(