In https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8928071888080982944 the atlas-paladin builder experienced a CreateTarballError. Fairly earl in the log the following is seen:

04:42:33: INFO: RunCommand: tar --sparse -I cat -cf /b/swarming/w/ir/tmp/t/cbuildbot-tmpfhFj3s/cbuildbot-autotestNUEnz6/autotest_packages.tar autotest/packages in /b/swarming/w/ir/cache/cbuild/repository/chroot/build/atlas/usr/local/build
tar: autotest/packages: file changed as we read it
04:50:03: WARNING: CreateTarball: tar: source modification time changed (see crbug.com/547055), retrying once

Then later:

04:55:20: ERROR: <class 'chromite.lib.cros_build_lib.CreateTarballError'>: return code: 1; command: tar --sparse -I cat -cf /b/swarming/w/ir/tmp/t/cbuildbot-tmpfhFj3s/cbuildbot-autotestNUEnz6/autotest_packages.tar autotest/packages
CreateTarball
Traceback (most recent call last):
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/parallel.py", line 441, in _Run
    self._task(*self._task_args, **self._task_kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/stages/artifact_stages.py", line 707, in BuildAutotestTarballs
    self._build_root, cwd, tempdir):
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/commands.py", line 2546, in BuildAutotestTarballsForHWTest
    BuildAutotestPackagesTarball(buildroot, cwd, tarball_dir),
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/commands.py", line 2455, in BuildAutotestPackagesTarball
    compressed=False)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/commands.py", line 2390, in BuildTarball
    inputs=input_list, **kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/cros_build_lib.py", line 1053, in CreateTarball
    raise CreateTarballError('CreateTarball', result)
CreateTarballError: return code: 1; command: tar --sparse -I cat -cf /b/swarming/w/ir/tmp/t/cbuildbot-tmpfhFj3s/cbuildbot-autotestNUEnz6/autotest_packages.tar autotest/packages
CreateTarball

04:55:20: INFO: Translating result <class 'chromite.lib.cros_build_lib.CreateTarballError'>: return code: 1; command: tar --sparse -I cat -cf /b/swarming/w/ir/tmp/t/cbuildbot-tmpfhFj3s/cbuildbot-autotestNUEnz6/autotest_packages.tar autotest/packages
CreateTarball
Traceback (most recent call last):
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/parallel.py", line 441, in _Run
    self._task(*self._task_args, **self._task_kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/stages/artifact_stages.py", line 707, in BuildAutotestTarballs
    self._build_root, cwd, tempdir):
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/commands.py", line 2546, in BuildAutotestTarballsForHWTest
    BuildAutotestPackagesTarball(buildroot, cwd, tarball_dir),
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/commands.py", line 2455, in BuildAutotestPackagesTarball
    compressed=False)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/cbuildbot/commands.py", line 2390, in BuildTarball
    inputs=input_list, **kwargs)
  File "/b/swarming/w/ir/cache/cbuild/repository/chromite/lib/cros_build_lib.py", line 1053, in CreateTarball
    raise CreateTarballError('CreateTarball', result)
CreateTarballError: return code: 1; command: tar --sparse -I cat -cf /b/swarming/w/ir/tmp/t/cbuildbot-tmpfhFj3s/cbuildbot-autotestNUEnz6/autotest_packages.tar autotest/packages
CreateTarball
 to fail.

Note a closed out bugs of a similar nature are https://crbug.com/855967 and https://crbug.com/892438.