Merge Request stuck with Rebase in progress

Summary

Unable to rebase two protected branches.

Steps to reproduce

So, I've got master and dev branches. Both protected. I'm using Merge commit with semi-linear history.

Master is ahead of dev some commits. I create a merge request from dev to master. I need to rebase dev onto master. I press the rebase button, go into the "rebase in progress" status. After some time, I either see the rebase button again, or that MR gets stuck with the "rebase in progress" message.

What is the current bug behavior?

Can't rebase

What is the expected correct behavior?

Rebase would work and I would be able to merge the branches. Or the rebase would fail. Definitely not going back to pressing the rebase button.

Output of checks

This bug happens on GitLab.com