Connection string is sometimes not available in ServiceBusTrigger

I don't have a final answer to this question, but I do want to share some details with other people experiencing the same problem. The problem seems to be isolated to v1 consumption based functions only. After upgrading my function to Azure Functions v2 and utilizing the new configuration system available there, I no longer experience the problem above. Since v1 is no longer the current version, I do not want to spend more time debugging into this, when v2 seems to be working.

According to this: you should be using the latest version 2.3.0 for nuget Microsoft.Azure.WebJobs.ServiceBus -Version 2.3.0

I would also check if it is an issue when running in consumption plan by hardcoding the connection to see if it is an issue reading the configuration of connection. And otherwise test it on app service plan.