Azure function - "Did not find any initialized language workers"

This is due to SDK version, I would suggest to deploy fresh function App in Azure and deploy your code there. 2 things to check :

1. Make sure your local function app SDK version matches with Azure function app.
2. Check python version both side.

This error is most likely github issue #4384. This bug was identified, and a fix was released mid-june 2020. Apps running on version 3.0.14063 or greater should be fine. List of versions is here.

You can use azure application insights to check your version. KUSTO Query the logs. The exception table, azure SDK column has your version.

If you are on the dedicated App Service plan, you may be able to "pull" the latest version from Microsoft by deleting and redeploying your app. If you are on consumption plan, then you may need to wait for this bugfix to rollout to all servers.

Troy Witthoeft's answer was almost certainly the right one at the time the question was asked, but this error message is very general. I've had this error recently on runtime 3.0.14287.0. I saw the error on many attempted invocations over about 1 hour, but before and after that everything worked fine with no intervention.

I worked with an Azure support engineer who gave some pointers that could be generally useful:

• Python versions: if you have function runtime version ~3 set under the Configuration blade, then the platform may choose any of python versions 3.6, 3.7, or 3.8 to run your code. So you should test your code against all three of these versions. Or, as per that link's suggestion, create the function app using the --runtime-version switch to specify a specific python version.

• Consumption plans: this error may be related to a consumption-priced app having idled off and taking a little longer to warm back up again. This depends, of course, on the usage pattern of the app. (I infer (but the Engineer didn't say this) that perhaps if the Azure datacenter my app is in happens to be quite busy when my app wants to restart, it might just have to wait for some resources to become available.). You could address this either by paying for an always-on function app, or by rigging some kind of heartbeat process to stop the app idling for too long. (Easiest with a HTTP trigger: probably just ping it?)

• The Engineer was able to see a lower-level error message generated by the Azure platform, that wasn't available to me in Application Insights: ARM authentication token validation failed. This was raised in Microsoft.Azure.WebJobs.Script.WebHost.Security.Authentication.ArmAuthenticationHandler.HandleAuthenticate() at /src/azure-functions-host/src/WebJobs.Script.WebHost/Security/Authentication/Arm/ArmAuthenticationHandler.cs. There was a long stack trace with innermost exception being: System.Security.Cryptography.CryptographicException : Padding is invalid and cannot be removed.. Neither of us were able to make complete sense of this and I'm not clear whether the responsibility for this error lies within the HandleAuthenticate() call, or outside (invalid input token from... where?).

The last of these points may be some obscure bug within the Azure Functions Host codebase, or some other platform problem, or totally misleading and unrelated.