App Platform caches static sites for up to 24 hours after their deletion. If you don’t remove a custom domain from a previous static site app before deleting it, the domain may still point to the old app for up to 24 hours after deleting the app. This can cause your domain to be unavailable to a new app until the DNS updates.
To avoid this, remove the custom domain from the old app before deleting it and then add the domain to the new app.