Hi there
I cannot see any relation between the HOST property and the shopOrigin cookie.
The reason why you get this error is because in _app.js the config object for the app-bridge-react Provider has undefined value for shopOrigin. In the demo app the value is set from the cookie named shopOrigin. Which, on the other hand, is set on afterAuth by koa-auth-shopify. Check those to track if shopOrigin is set properly.