TransportLayerManagerImpl uses invariant to enforce strict state transitions from kUninitialized -> kSetup -> kStarted -> kShutdown. However, the state can also transition to kShutdown from any state, and this can happen at any time (e.g. if a SIGTERM signal is handled). If such a signal happens to be received prior to startup being completed, an invariant can be triggered, crashing the process during shutdown.

We should relax these invariants to expect that shutdown may come at any time.

https://github.com/mongodb/mongo/blob/51a159d0d1b0d278a0107dffe474d597f91d361b/src/mongo/transport/transport_layer_manager_impl.cpp#L73