Jobs skipped randomly and no way to know why

Summary

We have a pipeline that triggers another pipeline in a different project at the end of the pipeline. For some reason (randomly), the job will be marked as skipped and doesn't run. How can we debug why the job was skipped?

Steps to reproduce

Create a pipeline and trigger another pipeline at the end of it, ours looks like this:

trigger_another_build:
  stage: publishing
  trigger: some_group/some_project
  only:
    refs:
      - master

What is the current bug behavior?

Job is skipped

What is the expected correct behavior?

Job runs

Relevant logs and/or screenshots

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Output of checks

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Results of GitLab environment info

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`sudo gitlab-rake gitlab:env:info`)

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`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

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sudo gitlab-rake gitlab:check SANITIZE=true)
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sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)