Inexplicable storage transactions from Azure Functions

Do you have AzureWebJobsDashboard enabled? If yes, you should disable it (delete the Connection String from the App Settings) and switch to application insights. This setting has been known to cause unexpected writes to storage which can't be properly explained.

https://github.com/Azure/Azure-Functions/issues/832

After weeks of investigation the Azure support team and I think we have found the line that causes the issue and this is it:

.AddJsonFile("local.settings.json", optional: true, reloadOnChange: true)

The config file was not published as part of the publish process and is not present in Azure. Experiments for now seem to confirm that when this is present the transactions spike and when not they are normal. This does not answer

• Why the bug happens at all
• Is it a regression in .NET Core or in the functions runtime?
• Why does the bug happen randomly and not on every run?

Note that testing this takes time as I have to wait for days for the random spike and I can never be sure if it is gone forever so I am not 100% sure that at some point in the future the spike won't happen again and turn out that the issue was something else.