GitLab reports it can't auto merge using a merge request but there is no conflict

Created by: cmsimike

There has been a bunch of times now where gitlab will say that a merge request cannot automatically be merged. So I close that merge request and ask the developer to clear out any merge conflicts that may arrise in their branch.

They do so, push their branch and create a new merge request but Gitlab still says it cannot auto merge. When I merge myself, there are no merge conflicts.

Is there something I'm missing here or are there any other reasons for Gitlab displaying the "cannot auto merge" message?