There was an issue impacting the dispersal of Weekly Postmaster Lockboxes when first released. You actually may be in a state where you are required to sign into a single character for the Lockbox to appear within the Postmaster. For now on, you should be receiving one lockbox to your postmaster weekly, no matter which character you log-in with. You may also inspect a character on Bungie.net or the Companion Application, and this will ensure delivery if you cannot sign-on to a console on a given week. We greatly apologize for the inconvenience.