StateMachine sometimes failed to evaluate system variables in log element.

<log label="Event name" expr="_event.name"/>

<state id="greenGoingRed">
                <onentry>
                    <send event="goRed" delay="1s"/>
                </onentry>
                <transition event="goRed" target="red">
                <log label="Event name" expr="_event.name"/>
                </transition>
</state>

 scxml.statemachine: "Event name" : "_event.name"