Impossible to commit using WebIDE because of "Branch has changed"
Summary
Currently it seems impossible to commit any changes using WebIDE. No matter of which option is selected, the modal window appears (see picture below) saying "Branch has changed\n This branch has changed since you started editing. Would you like to create a new branch?". And even when selecting to create a new one, it fails with the same message.
Steps to reproduce
Open some project in WebIDE. Do any change. Edit -> Review -> Commit. Write commit message. Select any of 3 available options (commit to branch, create new branch, or new branch and open MR). After clicking on commit button the modal window mentioned above appears.
What is the current bug behavior?
Blocks any commits from WebIDE.
What is the expected correct behavior?
Commit happens with respect to the commit option selected
Relevant logs and/or screenshots
Output of checks
This bug happens on GitLab.com
Possible fixes
(If you can, link to the line of code that might be responsible for the problem)