Log in https://logs.chromium.org/v/?s=chrome%2Fbb%2Fchromium.perf%2FAndroid_Nexus5X_WebView_Perf%2F2190%2F%2B%2Floading.mobile_9667968e-ed28-4cbf-83e5-bd6bc085c8f4 shows:

Traceback (most recent call last):
  RunBenchmark at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/story_runner.py:368
    expectations=expectations, max_num_values=benchmark.MAX_NUM_VALUES)
  Run at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/story_runner.py:216
    test, finder_options.Copy(), story_set)
  traced_function at /b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  __init__ at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/page/shared_page_state.py:86
    self.platform.network_controller.Open(wpr_mode)
  traced_function at /b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:52
    return func(*args, **kwargs)
  Open at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/core/network_controller.py:28
    self._network_controller_backend.Open(wpr_mode)
  Open at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/platform/network_controller_backend.py:72
    local_port=local_port, remote_port=None)
  Create at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/forwarders/android_forwarder.py:30
    return AndroidForwarder(self._device, local_port, remote_port)
  __init__ at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/forwarders/android_forwarder.py:91
    forwarder.Forwarder.Map([(remote_port or 0, local_port)], self._device)
  Map at /b/swarming/w/ir/third_party/catapult/devil/devil/android/forwarder.py:178
    formatted_output))
HostForwarderError: `/b/swarming/w/ir/third_party/catapult/devil/bin/deps/linux2/x86_64/forwarder_host --adb=/b/swarming/w/ir/third_party/catapult/devil/bin/deps/linux2/x86_64/bin/adb --serial-id=008671d42589ad4c --map 0 40537` exited with 1:
[0727/084724.603787:ERROR:daemon.cc(215)] Could not connect to daemon's Unix Daemon socket
Locals:
  device           : <devil.android.device_utils.DeviceUtils object at 0x7f212ece3990>
  device_port      : 0
  device_serial    : '008671d42589ad4c'
  exit_code        : 1
  formatted_output : "[0727/084724.603787:ERROR:daemon.cc(215)] Could not connect to daemon's Unix Daemon socket\n"
  host_port        : 40537
  instance         : <devil.android.forwarder.Forwarder object at 0x7f21440447d0>
  map_arg_list     : [u'--adb=/b/swarming/w/ir/third_party/catapult/devil/bin/deps/linux2/x86_64/bin/adb', '--serial-id=008671d42589ad4c', '--map', '0', '40537']
  map_arg_lists    : [[u'--adb=/b/swarming/w/ir/third_party/catapult/devil/bin/deps/linux2/x86_64/bin/adb', '--serial-id=008671d42589ad4c', '--map', '0', '40537']]
  map_cmd          : [u'/b/swarming/w/ir/third_party/catapult/devil/bin/deps/linux2/x86_64/forwarder_host', u'--adb=/b/swarming/w/ir/third_party/catapult/devil/bin/deps/linux2/x86_64/bin/adb', '--serial-id=008671d42589ad4c', '--map', '0', '40537']
  output           : "[0727/084724.603787:ERROR:daemon.cc(215)] Could not connect to daemon's Unix Daemon socket\n"
  port_pairs       : [(0, 40537)]
  tool             : <devil.android.valgrind_tools.base_tool.BaseTool object at 0x7f2144044d10>
(INFO) 2018-07-27 08:47:51,746 memory_debug.LogHostMemoryUsage:60  Used 1.7 GiB out of 31.4 GiB memory available.
(INFO) 2018-07-27 08:47:51,746 memory_debug.LogHostMemoryUsage:61  Memory usage of top 10 processes groups
(INFO) 2018-07-27 08:47:51,747 memory_debug.LogHostMemoryUsage:81  - python - 228.2 MiB - pids: ['52', '1103', '1112', '1139', '1149', '1337', '1338']
(INFO) 2018-07-27 08:47:51,747 memory_debug.LogHostMemoryUsage:81  - adb - 4.8 MiB - pids: ['1321']
(INFO) 2018-07-27 08:47:51,747 memory_debug.LogHostMemoryUsage:81  - su - 2.9 MiB - pids: ['51']
(INFO) 2018-07-27 08:47:51,747 memory_debug.LogHostMemoryUsage:81  - bash - 2.8 MiB - pids: ['1']
(INFO) 2018-07-27 08:47:51,747 memory_debug.LogHostMemoryUsage:81  - forwarder_host - 2.7 MiB - pids: ['2733']
(INFO) 2018-07-27 08:47:51,747 memory_debug.LogHostMemoryUsage:82  Current process:
(INFO) 2018-07-27 08:47:51,748 memory_debug._LogProcessInfo:41  63.0 MiB (pid=1338)
[  PASSED  ] 0 tests.
[  SKIPPED ] 74 tests.
View result at file:///b/swarming/w/it8jY3Ue/tmpCu6Libtelemetry/histograms.json

I wonder whether this is a device error?

This is the swarming build log: https://chrome-swarming.appspot.com/task?id=3ef3b9cf6dfa1510&refresh=10&show_raw=1

+jbudorick the error seems to be coming from forwarder2, any idea why could that be happening?