Code coverage visualization requires a reload to be displayed

Summary

After running a pipeline that generates a test coverage report, the Test coverage visualization on the lines of code is only displayed after explicitly reloading the MR diffs page.

Steps to reproduce

1. Create a project with unit tests
2. Add a job to generate a test coverage report
3. Create an MR with changes to the source code to generate a "Changes" (MR diff) tab
4. Wait until the pipeline generates the coverage report
5. Notice that the coverage visualization is only displayed after manually reloading the MR diffs

Example Project

The following private project on GitLab.com can be used to follow the reproduction steps above: https://gitlab.com/d1481/coverage-delay

What is the current bug behavior?

Test coverage visualization only becomes available after manually reloading the MR diffs page.

What is the expected correct behavior?

Test coverage visualization should be available as soon as the report is available, or at least shortly after, without manual intervention.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

A simple reload solves the problem, but customers are constantly reporting this as a problem.