When creating requisitions, sometimes the start and finish dates are blank at the requisition properties.
What does influence the requisition to be created with or without dates?

Any PPM release

The date population on the requisition is controlled by the team member allocation.
If the Default allocation % is zero and there is no segment with non zero allocation at team level, then the requisition is created with blank dates.
PPM assumes that if the team member does not have any allocation, the requisition will not have any allocation to replace to and therefore dates are blank.
When creating requisitions, please ensure that the team member does have some allocation.