Gantt Chart : Mirrored column as Timeline column doesn't seem to be working

I am trying to setup Gantt and Timeline View for our projects. I am trying to follow one of the monday template which has 3 different boards like EPIC, STORIES, SPRINTS. We want to have timeline view for each board so we can present it to different people. For example, we want to show EPIC timeline to investors so they can see product roadmap at top level. We have used mirrored columns for timeline.

Problem is that Timeline view is not working when I select “Sprint Timeline” column of EPIC board. This column is connected with Stories board and being derived from STORIES timeline.

Am I missing something here?