How do I diagnose 503 - Function host is not running (static web apps integrated functions)

Question

I have a static web app with C# integrated functions. Everything runs fine locally using the static web app CLI.

The github actions build completes and the app is published but all my functions get 503 Function host is not running responses.
I've tried turning on application insights and looking around the SWA portal but I can't find error the source anywhere

My host.json is just the standard/default:

{
    "version": "2.0",
    "logging": {
        "applicationInsights": {
            "samplingSettings": {
                "isEnabled": true,
                "excludedTypes": "Request"
            }
        }
    }
}

I'm in the dark on what is causing the deployed run time error.

Thanks