See https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8926553306670561712

Error message:
cmd=['git', 'push', 'origin', 'temp_auto_checkin_branch:refs/heads/master'], cwd=/b/swarming/w/ir/cache/cbuild/repository/manifest-versions-internal
Traceback (most recent call last):
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/failures_lib.py", line 230, in wrapped_functor
    return functor(*args, **kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/stages/sync_stages.py", line 751, in PerformStage
    next_manifest = self.GetNextManifest()
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/stages/sync_stages.py", line 863, in GetNextManifest
    build_id=build_id)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/lkgm_manager.py", line 427, in CreateNewCandidate
    raise manifest_version.GenerateBuildSpecException(last_error)
GenerateBuildSpecException: Failed to generate LKGM Candidate. error: return code: 1; command: git push origin temp_auto_checkin_branch:refs/heads/master
To https://chrome-internal.googlesource.com/chromeos/manifest-versions
 ! [rejected]                temp_auto_checkin_branch -> master (fetch first)
error: failed to push some refs to 'https://chrome-internal.googlesource.com/chromeos/manifest-versions'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

cmd=['git', 'push', 'origin', 'temp_auto_checkin_branch:refs/heads/master'], cwd=/b/swarming/w/ir/cache/cbuild/repository/manifest-versions-internal


It looks like an Infra failure.