Timeline shows subitems as unassigned

I am relatively new to monday.com and now experiencing with setting up a timeline view for my team.
I would like to show both items and sub-items on my timeline.
However, all my sub-items show up as unassigned in my timeline view, although there is a people column on the board for the sub-items as well.
I tried renaming the column from Person to Owner to Assignee - did not help.
How should I go about this?
How does monday.com map columns to the “assigned to” semantic?