Successful executions of unconditional stepdowns supercede stepdown attempts in response to replSetStepDown, but the execution of the command will not be killed if it wasn't issued by a client. Nodes attempting a priority takeover in pv0 send this command to the primary. A possible solution might be to make TopologyCoordinator::prepareForStepDownAttempt return an error if a stepdown has already completed (in addition to the existing stepdown-in-progress check.)