Subscriber missed message on rospy [closed]

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First, I made a rospy node A which has 5 subscribers, 1 service and 1 publisher. Then I made a system which included A and other nodes. When I tested the system, one of callbacks in node A missed topic(= the callback was node called) every time if I executed specific sequence. So, if you know why callback missed topic, could you tell me a reason?

As a unit test, when I tested the callback in node A with command line "rostopic pub", it received message every time. In above case of system test, the callback missed a topic. On the other hand, after missing a topic, if I sent missed topic manually, the callback received it.