People picker are not displaying all the users from the existing Synchronization Connections

Hello, I need help.

I have two domains, an old domain and a new domain that were are migrating to.

I have 2 connections for Users Synchronizations, one to the old domain and one to the new domain.

Here is what is happening: when I open people picker from any of the web applications only the users that existed in the old domain are showing and not the new users that are been added to the new domain. Basically people picker is displaying old data/users.

What can I do?