Why do some tasks have diagonal lines moving across them?

A diagonal lines animation on a card indicates that the task is currently being timed.
Whenever you or a team member start a timer on a task, the animation makes it easy to spot actively progressed items at a glance.

Having doubts as to who is timing a specific task?
Please refer to the task card’s time log:

To learn more about time tracking & reporting, please visit this guide.