Current QuicStreamFactory broadcasts platform signals to all alive sessions, which means a session that has gone away may attempt connection migration as well. 

Depends on what the signal is, a session that has gone away may consider skipping connection migration if the signals doesn't interrupt the session. E.g., a new network is made as default. 

The session, however, may still need to attempt connection migration on signals that will interrupt its connection such as the current network is being disconnected.