Hi,
Was the prefabA instance generated because it received that button click event?
you are likely within a typical race condition with the event data and the events themselves.
event data is a public static variable, which means it's the same for everyone regardless of what even has been fired, so in your case, you are likely in the case where playmaker has updated the event data because it received the click event, but your fsm are still proceeeding other event thinking they are still in that "context".
to solve this, wait the next frame for your prefabA instance to fire that event, it tempers this kind of race condition.
try to also fill the event data GameObject variable with the owner of who is sending this event, this could work in your case, instead of relying on the event data sender variable.
Bye,
Jean