Bartłomiej Piotrowski commented:
It seems to be GitLab issue we're seeing also in other projects. You can work it around by setting a different merging method, but other than this, we're waiting for an answer from GitLab team.
Some of the upstream issues: https://gitlab.com/gitlab-org/gitlab/-/issues/217558 https://gitlab.com/gitlab-org/gitlab/-/issues/30141