We're currently experiencing an issue with the new story button not responding on the latest version of the Medium iOS app. Existing drafts can still be edited and published. As a workaround, you can create a new story using Medium on your desktop computer or the Android app, and then edit it from your iOS app. To learn more, see: https://help.medium.com/hc/en-us/articles/225168768
We apologize for the inconvenience and thank you for your patience as our engineers are working to resolve this bug.