E.g. https://uberchromegw.corp.google.com/i/chromeos/builders/tricky-chrome-pfq/builds/2320

12:42:41: WARNING: Exception is not retriable return code: 3; command: /b/cbuild/internal_master/chromite/third_party/swarming.client/swarming.py run --swarming chromeos-proxy.appspot.com --task-summary-json /tmp/cbuildbot-tmpCW43CU/tmpr9TI2y/temp_summary.json --raw-cmd --task-name tricky-chrome-pfq/R55-8776.0.0-rc1-bvt-inline --dimension os Ubuntu-14.04 --dimension pool default --print-status-updates --timeout 14400 --io-timeout 14400 --hard-timeout 14400 --expiration 1200 -- /usr/local/autotest/site_utils/run_suite.py --build tricky-chrome-pfq/R55-8776.0.0-rc1 --board tricky --suite_name bvt-inline --pool bvt --num 6 --file_bugs True --priority PFQ --timeout_mins 180 --retry False --minimum_duts 4 --suite_min_duts 3 --offload_failures_only False -m 75912081
Priority was reset to 100
Triggered task: tricky-chrome-pfq/R55-8776.0.0-rc1-bvt-inline
Waiting for results from the following shards: 0
Waiting for results from the following shards: 0
Waiting for results from the following shards: 0
chromeos-server31-197: 3119a74bc5f24510 3
  Autotest instance: cautotest
  09-06-2016 [11:49:47] Created suite job: http://cautotest.corp.google.com/afe/#tab_id=view_job&object_id=75912081
  @@@STEP_LINK@Link to suite@http://cautotest.corp.google.com/afe/#tab_id=view_job&object_id=75912081@@@
  Unhandled run_suite exception: Timeout occurred- waited 1800 seconds.
  Traceback (most recent call last):
    File "/usr/local/autotest/site_utils/run_suite.py", line 1710, in main
      (code, output_dict) = main_without_exception_handling(options)
    File "/usr/local/autotest/site_utils/run_suite.py", line 1596, in main_without_exception_handling
      while not afe.get_jobs(id=job_id, finished=True):
    File "/usr/local/autotest/server/frontend.py", line 292, in get_jobs
      jobs_data = self.run('get_jobs', **dargs)
    File "/usr/local/autotest/server/cros/dynamic_suite/frontend_wrappers.py", line 111, in run
      self, call, **dargs)
    File "/usr/local/autotest/site-packages/chromite/lib/retry_util.py", line 86, in GenericRetry
      time.sleep(sleep_time)
    File "/usr/local/autotest/site-packages/chromite/lib/timeout_util.py", line 62, in kill_us
      raise TimeoutError(error_message % {'time': max_run_time})
  TimeoutError: Timeout occurred- waited 1800 seconds.
  Will return from run_suite with status: INFRA_FAILURE


This looks like a real time-out, since on successful run hw-test takes much less time.