Vault should return users only once they can be used
Currently, the Vault Plugin immediately returns the MongoDB users after they are created in Atlas. However, they have not been rolled out to the actual nodes yet. Immediately using them on a cluster will fail.
Unfortunately MongoDB does not want to provide a fixed maximum time to wait, as the time apparently depends on many factors, including how many clusters are in a project, or if there are other changes being rolled out.
It would be a much simpler and better user experience if the Vault plugin would only return the user once it is actually usable, even if that means a longer call.