Please do as follows to resolve this:
Go to the Leave module, Setup, Leave Policy.
Check the leave policy, whether the allocation table for Maternity leave is set as System MOM or manually created.
If it is manually created, then go to Setup, Leave Type, select this leave type.
Change the Maternity Leave Function from Others to Maternity MOM.
Go to Setup, Leave Policy, and the system will update the allocation table for Maternity as System MOM. (16 weeks * Calendar ID belongs to staff)
Go to Process Leave and Recalculate the Maternity Leave.