The failure starts showing on PFQ on 12/02. See an example failed build: https://uberchromegw.corp.google.com/i/chromeos/builders/caroline-chrome-pfq/builds/910

Selected error messages:
Restoring previous backed up file (/b/build/site_config/.boto.bak)
Failure: EOF when reading a line.
cmd=['/tmp/cbuildbot-tmp_ilU_C/chrome-sdk-cache53nna8/cache/common/gsutil_4.27.tar.gz/gsutil/gsutil', '-o', 'Boto:num_retries=10', 'config'], extra env={'BOTO_CONFIG': '/b/build/site_config/.boto'})
04:23:54: ERROR: cros chrome-sdk failed before completing.
cros: Unhandled exception:
Traceback (most recent call last):
  File "/b/c/cbuild/repository/chromite/bin/cros", line 169, in <module>
    DoMain()
  File "/b/c/cbuild/repository/chromite/bin/cros", line 165, in DoMain
    commandline.ScriptWrapperMain(FindTarget)
  File "/b/c/cbuild/repository/chromite/lib/commandline.py", line 911, in ScriptWrapperMain
    ret = target(argv[1:])
  File "/b/c/cbuild/repository/chromite/scripts/cros.py", line 66, in main
    code = _RunSubCommand(subcommand)
  File "/b/c/cbuild/repository/chromite/scripts/cros.py", line 51, in _RunSubCommand
    return subcommand.Run()
  File "/b/c/cbuild/repository/chromite/cli/cros/cros_chrome_sdk.py", line 1041, in Run
    use_external_config=self.options.use_external_config)
  File "/b/c/cbuild/repository/chromite/cli/cros/cros_chrome_sdk.py", line 133, in __init__
    self.gs_ctx = gs.GSContext(cache_dir=cache_dir, init_boto=internal)
  File "/b/c/cbuild/repository/chromite/lib/gs.py", line 582, in __init__
    self._InitBoto()
  File "/b/c/cbuild/repository/chromite/lib/gs.py", line 650, in _InitBoto
    self._ConfigureBotoConfig()
  File "/b/c/cbuild/repository/chromite/lib/gs.py", line 641, in _ConfigureBotoConfig
    print_cmd=False)
  File "/b/c/cbuild/repository/chromite/lib/gs.py", line 878, in DoCommand
    raise GSCommandError(e.msg, e.result, e.exception)