Is it required to issue a shipment conformity certificate for non regulated products, and what are the consequences of not issuing it?

Yes it is required to issue a shipment conformity certificate for imported & non regulated produ ...

Is registration of self-declaration and issue the shipment certificate for imported non-regulated products considered mandatory for clearing shipments? or is it optional?

Self-declaration of non-regulated products is required, and a shipment certificate should be issued.