EventEmitter constructor was not being called in many places. It did work due to the EventEmitter3 constructor being empty, but we can't rely on that.

lib/util/failcounter.js

@@ -3,6 +3,7 @@ var util = require('util')
 var EventEmitter = require('eventemitter3').EventEmitter
 
 function FailCounter(threshold, time) {
+  EventEmitter.call(this)
   this.threshold = threshold
   this.time = time
   this.values = []