Public holidays display a duration of 0 hours if the Entitlement Includes Public Holidays option is not selected in the employee's planner Settings.
If the public holiday duration displays a different number of hours than what the employee is working daily, this is because the employee was assigned to a different working pattern on the date the public holiday falls on.
To check this:
Click Access Button
then click Employee.
Select the relevant employee then click Planner.
On the work pattern dropdown, click the Clock icon to see the history.
Check if the employee was assigned to a different work pattern for those dates.
📌Note: You can also click on the public holiday and manually amend the duration field.