Missing Functions in isolated worker function app

Hello!

I upgraded from an in-process modell to isolated worker.
After the deployment everything worked and the functions were able to be invoked, but I got an error message saying: Referenced bundle Microsoft.Azure.Functions.ExtensionBundle of version 1.8.1 does not meet the required minimum version of 2.6.1.
So I added the extension bundle in the host.json:

  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.*, 5.0.0)"
  }

After redeploying the function app, all functions went missing and could not be invoked anymore.