It appears 2 shards timed out and the tests in those shards weren't counted? It also looks like the massive flakes started around https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win10%20Tests%20x64%20%28dbg%29/1962. While I didn't find any suspects in build 1962, there was a catapult roll in 1961 - I wonder if that could be related. +sullivan@ who was TBR on the catapult roll patch.

Aforementioned roll patch: https://chromium-review.googlesource.com/c/chromium/src/+/1141465

Many tests failed with one of two stack traces below:

 Traceback (most recent call last):
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\testing\tab_test_case.py", line 25, in setUp
      self._RestartBrowser()
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\testing\tab_test_case.py", line 45, in _RestartBrowser
      self._tab = self._browser.tabs[0]
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\browser\tab_list.py", line 18, in __getitem__
      return self._tab_list_backend.__getitem__(index)
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_backend_list.py", line 62, in __getitem__
      index, repr(self._filtered_context_ids)))
  DevtoolsTargetCrashException: Web content with index 0 may have crashed. filtered_context_ids = []

----

 Traceback (most recent call last):
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\testing\tab_test_case.py", line 20, in setUp
      self._browser.tabs.New()
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\browser\tab_list.py", line 9, in New
      return self._tab_list_backend.New(timeout)
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\backends\chrome\tab_list_backend.py", line 43, in New
      return self.GetBackendFromContextId(context_id)
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_backend_list.py", line 75, in GetBackendFromContextId
      context_id)
    File "C:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\devtools_client_backend.py", line 573, in GetInspectorBackend
      raise KeyError('Cannot find a context with id=%s' % context_id)
  KeyError: u'Cannot find a context with id=4051D55538933CE4F7C984D5A8F02B1F'

This doesn't appear to be an infra issue, removing the component. If you need our help though, please add Infra>Client>Chrome back and mark it Untriaged. Thanks!