You are building an industrial IoT solution where, using several S1 IoT hubs, you collect telemetry data from a number of field sensors. The data collected by the IoT hubs must be forwarded to a Storage Container and to be published to a Service Bus topic to make them available for consumer services. You have configured the message routes and queries for the two endpoints but while testing, you notice that some of the messages don’t reach any of the configured targets, they are lost. 
What is the recommended solution?

Answer options:

A.Configure a route to the messages/events endpoint
B.Makes sure the fallback route is enabled
C.Makes sure the fallback route is disabled
D.Make sure the feedback queue is enabled

Correct Answer: B
Option A is incorrect because the messages/events is the default built-in endpoint of the IoT hub.Howevers, once a route is created, data stops flowing to this endpoint. While you can create an explicit route there, it is recommended to enable the fallback route which automatically directs all messages not caught by the queries of the other routes to messages/events.
Option B is CORRECT because the fallback route has to be enabled so that messages that don`t satisfy query conditions on any of the existing routes are forwarded to the built-in-Event Hubs endpoint (messages/events).
Option C is incorrect because once a route is created, data stops flowing to the built-in-endpoint, unless a route is created to that endpoint, or the fallback route is enabled. It is the disabled fallback route that probably caused the problem.
Option D is incorrect because the feedback queue is for the cloud-to-device message direction, i.e. it doesn’t play any role here.
Diagram: 

References: 

https://docs.microsoft.com/en-us/azure/iot-hub/iot-hub-devguide-messages-d2c#fallback-route
https://docs.microsoft.com/en-us/rest/api/iothub/iothubresource/createorupdate#fallbackrouteproperties