@stewart, jahi k , Thanks for posting this good question.
1/3:
Typically, the default app appears because you either haven't deployed your app code to App Service, or App Service failed to find your app code and ran the default app instead. I understood that you have already reviewed the deployment code and default document. I’m not sure about the deployment framework of your WebApp. Kindly try these steps to further narrow-down the issue.
Try restarting the WebApp (if not done already(, wait 15-20 seconds, and then check.
Are you using Linux or Windows App Service?
**d:\home\site\wwwroot** - is the location where the sites files are saved.
Access Kudu Console and see if all the deployments are available as expected.
On App Service WebApp, you can copy (drag and drop the file into the site root/ d:\home\site\wwwroot\ folder) the via Kudu console (https://<yourwebpp-name>.scm.azurewebsites.net/) (\“Debug console”).