We are experiencing the same issue for one of our clients. I created a new custom Task Card form (Unified Interface) and didn't even add any User-related field to the form. A User name (Owner? Last Modified By?) is still being mapped to the top line of the Task card in the Timeline. There does not appear to be any workaround for this. No alternative but to tell our client it's a bug. Please give this a higher priority to be fixed.
Is any solution provided for showing (and at the same time filtering and sorting) Due Date om the first line of the activities in Timeline?