I created simple node.js application (source code from here https://azure.microsoft.com/en-us/blog/visual-studio-code-and-azure-app-service-a-perfect-fit/)
var h
I had the same issue. In my case my launch.json had following line
"program": "${workspaceFolder}\\index.js"
My active code that I tried to debug was in app_v2.js , so I updated it to following, and then debug worked.
"program": "${workspaceFolder}\\app_v2.js"