Have just seen the preview of issues/PRs that appears to the right of the screen when you click on one on a project board.
For managing projects, it would be great if the Milestone appeared (and be editable) on here, like Assignees, Labels and Projects.
It also appears that the milestone has gone missing from the issue/PR when dropped into a project. Again this would be really useful. (My team and I seem to remember it being there in the past.)