"An error occurred while fetching the pipeline." for multi-project pipeline trigger of same pipeline

Summary

In a rather complex CI pipeline on a hosted GitLab instance I ran into this issue. Fortunately, it can be reproduced easily on gitlab.com, too. I created a public repository for reference: https://gitlab.com/slowjoe/pipeline-test

A similar error occurs when accessing the jobs of the 2nd stage on the pipelines overview page:

Steps to reproduce

Define a CI pipeline like this and execute it:

stages:
  - build
  - deploy

build:
  stage: build
  script: |
    echo "Build completed."
  rules:
    - if: '$CI_PIPELINE_SOURCE != "parent_pipeline" && $CI_PIPELINE_SOURCE != "trigger"'

trigger-multi-project:
  stage: deploy
  trigger:
    project: $CI_PROJECT_PATH
    strategy: depend
  rules:
    - if: '$CI_PIPELINE_SOURCE != "parent_pipeline" && $CI_PIPELINE_SOURCE != "trigger"'
      when: manual
      allow_failure: true

start:
  stage: deploy
  script: |
    echo "Let's go!"
  rules:
    - if: '$CI_PIPELINE_SOURCE == "parent_pipeline" || $CI_PIPELINE_SOURCE == "trigger"'
      allow_failure: false

Example Project

https://gitlab.com/slowjoe/pipeline-test

What is the current bug behavior?

UI displays error message instead of the job details.

What is the expected correct behavior?

Display jobs, so I can trigger them manually.

Relevant logs and/or screenshots

No logs, but screenshots. See above.

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

n/a

Results of GitLab application Check

n/a

Possible fixes

n/a