Stop environment job not automatically running once MR has been merged

I currently have a pipeline running which deploys review apps to an environment. I am using the “Merged results pipelines” feature and so a pipeline is only run once a merge request has been opened for a particular branch. I also have the merge trains feature enabled as well if that makes any difference.

The problem I am having, is that the “stop environment” job is not being automatically triggered once the merge request has been merged into main branch.

Here is the related section of my gitlab-ci.yml file:

.Deploy Review:
  stage: Deploy
  image:
    name: ...
    entrypoint: [""]
  dependencies: []
  script:
    - echo "Hi"

Deploy Review:
  extends: .Deploy Review
  environment:
    name: $CI_COMMIT_REF_SLUG-$CI_MERGE_REQUEST_IID-review/app
    url: <url>
    deployment_tier: development
    on_stop: Teardown Review
  rules: !reference [.merge-request-with-app-changes, rules]

.Teardown Review:
  stage: Deploy
  image:
    name: ...
    entrypoint: [""]
  variables:
    GIT_STRATEGY: none
  script:
    - echo "Teardown..."
  when: manual

Teardown Review:
  extends: .Teardown Review
  dependencies:
    - Deploy Review
  needs: ["Deploy Review"]
  environment:
    name: $CI_COMMIT_REF_SLUG-$CI_MERGE_REQUEST_IID-review/app
    action: stop
  rules: !reference [.merge-request-with-app-changes, rules]

And then my reference rules are in another file like so:

.app-only-code-changes:
  rules:
    - changes: &only_app_code_changes_array
      - app/**/*

.merge-request-with-app-changes:
  rules:
    - if: '$CI_MERGE_REQUEST_EVENT_TYPE == "merged_result"'
      changes: *only_app_code_changes_array

I’m also wondering which pipeline should actually be responsible for running the “stop environment” job? Should it be triggered from the last merge results pipeline for that merge request?

Any advice is much appreciated.