Ensure that the rule is assigned to the employees in Accrual Settings based on the filters assigned to Company, Location, Department and Employment type.
If one or more of the filters doesn't apply to a user the accrual will not add for them.
When you're updating the employee record, check the accrual settings filters apply to their updated record so it will continue to add entitlement for the employee going forward.
📌Note: You would need to ensure you have the in use option ticked for the Accrual function to work, this is in the main page along with the rules you create.