I have a script that checks for required "config vars" in heroku. I added it to a Procfile so that it will run in the heroku "release phase". I tested it by removing one of the required "config vars" from a deployed app. The logs show that the release phase one-off dyno ran the script and didn't find any missing "config vars". Is it possible that the one-off dyno created for the release phase still has all of the "config vars" from before? I've combed through the heroku documentation but there is no mention of when the variable is actually removed.
I discovered that this was an issue with the format of my environment variables. The release phase doesn't include environment variables that contain a dot character . For reference, I was using the Ruby buildpack and accessing the config vars with the ENV class.