Here are some example failures:
https://uberchromegw.corp.google.com/i/chromium.perf/builders/Mac%2010.10%20Perf%20%283%29/builds/4174/steps/blink_perf.paint.reference/logs/stdio
https://uberchromegw.corp.google.com/i/chromium.perf/builders/Mac%2010.10%20Perf%20%283%29/builds/4134/steps/blink_perf.paint.reference/logs/stdio
https://uberchromegw.corp.google.com/i/chromium.perf/builders/Mac%2010.10%20Perf%20%283%29/builds/4172/steps/smoothness.tough_canvas_cases/logs/stdio
https://uberchromegw.corp.google.com/i/chromium.perf/builders/Mac%2010.10%20Perf%20%283%29/builds/4173/steps/power.top_25.reference/logs/stdio

Of the couple I've looked at, they all fail with this error:

Traceback (most recent call last):
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/internal/story_runner.py", line 79, in _RunStoryAndProcessErrorIfNeeded
    state.WillRunStory(story)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 75, in traced_function
    return func(*args, **kwargs)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/page/shared_page_state.py", line 225, in WillRunStory
    self._StartBrowser(page)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 75, in traced_function
    return func(*args, **kwargs)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/page/shared_page_state.py", line 185, in _StartBrowser
    self._browser = self._possible_browser.Create(self._finder_options)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome/desktop_browser_finder.py", line 68, in Create
    browser_backend, self._platform_backend, self._credentials_path)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/internal/browser/browser.py", line 55, in __init__
    self._browser_backend.Start()
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 75, in traced_function
    return func(*args, **kwargs)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome/desktop_browser_backend.py", line 294, in Start
    self._WaitForBrowserToComeUp()
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py", line 75, in traced_function
    return func(*args, **kwargs)
  File "/b/c/b/Mac_10_10_Perf__3_/src/third_party/catapult/telemetry/telemetry/internal/backends/chrome/chrome_browser_backend.py", line 161, in _WaitForBrowserToComeUp
    raise exceptions.BrowserConnectionGoneException(self.browser, e)
BrowserConnectionGoneException: Timed out while waiting 60s for HasBrowserFinishedLaunching.

Looks like a bad bot?