Perhaps check if each client has unique hardware key (Xibo player options -> advanced tab -> Display ID)
I added a new Player and it went straight to "Display is active and ready to start"? I'm using an imaged/cloned version of Windows and all my Players show up as the same display in the Xibo CMS?
I assume there is at least one display record on displays page in CMS, otherwise you couldn’t grant them a display licence - which means other clients most likely have the same hardware key.