In order to gossip the different components of the vector clock, we attach them to both commands requests and their replies before to send them over the wire. This is done by calling the VectorClock::gossipOut() function.
This function inspects the tags of the current session to decide which components of the vector clock will be gossiped. If no session is found the default tags (passed to the function) will be used for this decision.
Now the problem is that a session can exists but it can be still in the early kPending state, in such a case it won't have any of the other tags.
This case it is not considered by the VectorClock::gossipOut() function. In fact if a session in a pending state is found we always threat the communication as external and the the default tags (passed to the function) will be ignored.
This results in the VectorClock components not being gossiped on all the newly started sessions.