Azure YAML Deployment failing with "Error: Failed to deploy web package to App Service. Conflict (CODE: 409)"

Restarting the App Service solved my problem.

My App Service Plan was already a paid subscription and there was no issue with the capacity. I just restarted the App Service and everything worked fine.

So after a lot of discussion with MS support, Here is the ticket

It transpires that the real issue is that my App Service Plan was at capacity. In development we were using the free service and there are limits. We had hit this limit and the message was really a red herring and not the real problem at all.

Anyway, I upgraded to the first tier of paid subscription and everything is now working.