Issue
Visitors to my Private Spaces app sometimes have a problem in viewing the page and see "404 Not Found" errors on some of assets. It seems to happen when the app is being deployed.
Resolution
Visitors to the app see "404 Not Found" errors when it first fetches a response from a newly restarted web dyno for the Private Spaces going through rolling deploy and a request to an asset of the new version of the app is routed to a web dyno that is yet to be restarted.
While Heroku doesn't have a good solution for this problem, a customer solved the problem by placing a CDN in front of the app: https://buildingvts.com/serving-assets-while-rolling-your-deploys-c656ce6a2123