You have maintained the parameters for simple discontinuation in the material master of a component.

If the available stock is zero and the discontinuation date is in the past, the material requirements planning (MRP) process will be affected. MRP will not create any planned orders or purchase requisitions for the discontinued component. Instead, it will create a discontinuation indicator in the MRP list and a discontinuation message in the exception message list. This will inform the planner that the component is no longer available and that a follow-up material should be used instead. References: [SAP Help Portal] - Discontinuation of Materials.