Browsers would deal with it just fine (assuming the site is down hard and not responding with errors). Its some of the API tools and old libraries that may not

Browsers would deal with it just fine (assuming the site is down hard and not responding with errors). Its some of the API tools and old libraries that may not. They would need retry logic that mimics the browser cycling through multiple A records. OTOH, API tools that have retry logic would just keep trying until the errors clear up. A browser will stop retrying when something responds unless there was javascript running in memory that had retry logic. If there are errors, the site would need to be modified to not respond if broken and unable to proxy to a working origin. Perhaps CF have not coded their proxies in this manor.