MR shows zero commits and empty changes tab

Summary

After merging an MR, the commits that appear on the main branch are not displayed in the MR itself. The MR shows zero commits and the Changes tab appears empty, despite the MR containing 3-4 commits.

Steps to reproduce

1. Navigate to this specific MR: gitlab-org/technical-writing/docs-gitlab-com!1645 (merged)
2. Check the Commits tab → Shows 0 commits
3. Check the Changes tab → Shows empty
4. Navigate to main branch → Commits are visible

What is the current bug behavior?

• MR displays 0 commits
• Changes tab is empty
• Commits are visible on main after merge

What is the expected correct behavior?

• MR should display all commits (3-4 commits in this case)
• Changes tab should show the diff of all changes

Additional observations

• When visiting the MR and clicking the diff versions dropdown, all versions show as selected (should only select latest by default)
• When clicking "latest" version, the diff displays correctly. The commits are still not displayed.
• Not related to diff commit deduplication work (only enabled for 3 internal projects as of today, #527239)

Relevant logs and/or screenshots

Possible fixes

Patch release information for backports

If the bug fix needs to be backported in a patch release to a version under the maintenance policy, please follow the steps on the patch release runbook for GitLab engineers.

Refer to the internal "Release Information" dashboard for information about the next patch release, including the targeted versions, expected release date, and current status.

High-severity bug remediation

To remediate high-severity issues requiring an internal release for single-tenant SaaS instances, refer to the internal release process for engineers.