Dashboard users will receive an email titled "Did you release your app in Leanplum development mode?" when the developer users in the Leanplum dashboard reach 1000.
This is done to bring awareness to the team and ensure the app was not accidentally released with the SDK configured for development mode
It is possible the number of developer users increases gradually during testing when new users area created. If this is the case, it is recommended to cleanup unused test users and delete them as described in this article: