Standard Delivery option Suddenly Not available for Asins.... only Guaranteed delivery is Showing in Amazon Website and App For all our Listings

Since yesterday Standard Delivery option has not available in our asins , instead of that Shows only guaranteed Delivery alone, Except Guaranteed Delivery Locations Rest of all Locations are Showing Not Deliverable to this Pincode Choose a Different Pincode, What is the issue with Amazon Buyer Portal , Why Suddenly it Happens of All our Listings Can Anyone help us