It's related to the immutability of releases. When you change settings in a project, eg. variables, it doesn't affect existing releases. Generally this is good, as you want to guarantee repeatable deployments.
But if a project hasn't yet been successfully deployed, or you're still getting it set up, you'll need to create new releases and the immutability can catch you out.
We now notify when project settings have been changed, so that you can go and create a new release if needed.
Product Manager - Deployment Manager