Milestone issue board does not display all issues when split by epic

I’ve noticed an odd possible bug when using my gitlab issue boards. When I look at my milestone board without grouping the issues, all are visible. However, when I group by Epic, there are 7 open issues missing from the milestone board. I should have 27 open issues for the current milestone, and that is stated at the top of the milestone in both cases. However, when grouped by epic, only 20 issues are visible. All issues have milestones and epics assigned, so that should not be the issue.

Has anyone else experienced this? Is it a new bug, or something I’m doing wrong?