projects/:id/mirror/pull returns 200, but doesn't do anything

Summary

When I try to use the API to force update a mirrored project I get a 200 status code, but the mirror doesn't get updated.

Steps to reproduce

I have a mirrored project (id: 5130849) and I try to update it through the API using a token that I generated. The API call looks like this:

curl -XPOST https://gitlab.com/api/v4/projects/5130849/mirror/pull?private_token=XXXXXXXXXX

Example Project

https://gitlab.com/T-vK/ungoogled-chromium-mirror/

What is the current bug behavior?

The API doesn't work as expected. And besides that I should mention that the manual update button always says Update scheduled... and is unclickable. And it does not update automatically once per hour. It's more like once every 1.5 hours.

What is the expected correct behavior?

The described API works and the Update button can be clicked.

Output of checks

This bug happens on GitLab.com