iphone error - webdriverserver out of range index

I have a iPhone 6 running on a Mac Mini. I’ve followed the instructions for the mobile agent setup. The iPhone is able to get the new request but has trouble completing it.

It seems to be getting an out of range index error from webdriverserver. Any idea what may be causing this?

E Dec_01_10:52:37.362 process_utils.js:372 Socket. : /Users/ptg/wpt/agent/js/lib/ios/video/xrecord STDERR: 2016-12-01 10:52:37.362 xrecord[11115:6312282] Recording started. Hit ctrl-C to stop.
I Dec_01_10:52:37.474 process_utils.js:366 unknown : Spawning: ‘/Users/ptg/wpt/agent/js/lib/ios/idevice/Darwin x86_64/ios_webkit_debug_proxy’ -c c02bf95adcf38df47b5effb6fa1334d7b5affc1a:6700
E Dec_01_10:52:39.358 process_utils.js:372 Socket. : /Users/ptg/wpt/agent/js/lib/ios/video/xrecord STDERR: 2016-12-01 10:52:39.358 xrecord[11115:6312517] captureOutput Started callback
I Dec_01_10:52:41.930 wd_server.js:446 WebDriverServer. : Test started
I Dec_01_10:52:43.151 wd_server.js:356 WebDriverServer.onDevToolsMessage_ : DevTools message: {“method”:“Page.loadEventFired”,“params”:{“timestamp”:1.054152435157448}}
E Dec_01_10:52:44.373 wd_server.js:1228 WebDriverServer. : Top-level process uncaught exception: out of range index
E Dec_01_10:52:44.375 wd_server.js:217 WebDriverServer. : Exception from “Run test”: RangeError: out of range index
E Dec_01_10:52:44.379 wd_server.js:1214 WebDriverServer. : App uncaught exception event: [{“webdriver_promise_error_”:true}]
C Dec_01_10:52:44.379 wd_server.js:1637 WebDriverServer.onUncaughtException_ : Uncaught exception: RangeError: out of range index
at RangeError (native)
at fastCopy (/Users/ptg/wpt/agent/js/node_modules/ws/lib/Receiver.js:296:24)
at Receiver.add (/Users/ptg/wpt/agent/js/node_modules/ws/lib/Receiver.js:82:3)
at Socket. (/Users/ptg/wpt/agent/js/node_modules/ws/lib/WebSocket.js:482:14)
at emitOne (events.js:96:13)
at Socket.emit (events.js:188:7)
at readableAddChunk (_stream_readable.js:177:18)
at Socket.Readable.push (_stream_readable.js:135:10)
at TCP.onread (net.js:542:20)
==== async task ====