Creating a merge request branch for a project creates a fork of the project

Summary

Creating a merge request branch for a project creates a fork of the project

Steps to reproduce

Open Marketing, Digital Experience, about.gitlab.com Repository for FR-FR content.

Try to open an MR with single file editor.

I then encounter different issues:

Problem 1) It won't let me create the MR and will tell me "You are trying to update a file that has changed since you started editing it."
Clearing cache didn't fix it.
Same issue in other browsers (tested in Safari)

Problem 2) Create an MR with single file editor doesn't work and creates a fork of the project. Example: gitlab-com/marketing/digital-experience/about-gitlab-com!4047 (closed)

Open an MR with WEB IDE seems to work properly.

Example Project

What is the current bug behavior?

Create an MR in single file editor doesn't work.

What is the expected correct behavior?

Create an MR in single file editor work.

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

     (For installations with omnibus-gitlab package run and paste the output of: \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\`sudo gitlab-rake gitlab:env:info\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\`)  (For installations from source run and paste the output of: \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\`)      

Results of GitLab application Check

Expand for output related to the GitLab application check

    (For installations with omnibus-gitlab package run and paste the output of: \\\\\\\\\\\\\\\`sudo gitlab-rake gitlab:check SANITIZE=true\\\\\\\\\\\\\\\`)  (For installations from source run and paste the output of: \\\\\\\\\\\\\\\`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

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.