In the 10.x versions of TraderWorkstation (TWS) and IBGateway software, non-simultaneous clients with ID numbers different from the first don't receive price ticks for a given stock after requesting them.
Note: additional public discussion is occuring here.
After signing into the IBGateway (or TWS) application, a client program can't get ticks for a stock unless subsequent invocations use the same client ID as the first instance which requested those ticks.
In other words, during the same login session (without exiting the IBGateway/TWS software)... if a client program connects with ID #5 and receives ticks for IBM and subsequently exits, then any new client that requests ticks for IBM needs to connect using ID #5. If the original client ID number is not used, price ticks for IBM won't be received.