Why is my location-based shipping rule not working anymore?

Hello.

I’m facing issues with shipping.

I have 6 locations on my store.Each location is stocked differently.

In order to block orders for product which are not stocked in a location, we created shipping zones for each location.

So If a location does not have a product stocked, the shipment cannot be done, and the order cannot be placed. The attached message would appear during checkout.

This was working fine but suddenly this week, it is not anymore. Customers are able to place orders to a location where the product is not stocked. The error message does not appear anymore. I checked the setup and nothing changed! Can anyone help!?