At least two builders this week failed for this reason:
https://luci-milo.appspot.com/buildbot/chromeos/peach_pit-paladin/16558
https://luci-milo.appspot.com/buildbot/chromeos/wolf-paladin/15170

The error log is:
Test failed due to Unexpected files/perms in stateful. Exception log follows the after_iteration_hooks.
08/01 19:49:27.405 DEBUG|              test:0392| starting after_iteration_hooks
08/01 19:49:27.406 DEBUG|             utils:0212| Running 'mkdir -p /usr/local/autotest/results/default/security_StatefulPermissions/sysinfo/iteration.1/var/spool'
08/01 19:49:27.416 DEBUG|             utils:0212| Running 'rsync --no-perms --chmod=ugo+r -a --safe-links --exclude=/crash/**autoserv* --exclude=*.core /var/spool/crash /usr/local/autotest/results/default/security_StatefulPermissions/sysinfo/iteration.1/var/spool'
08/01 19:49:27.429 DEBUG|             utils:0212| Running 'rm -rf /var/spool/crash/*'
08/01 19:49:27.442 DEBUG|             utils:0212| Running 'logger "autotest finished iteration /usr/local/autotest/results/default/security_StatefulPermissions/sysinfo/iteration.1"'
08/01 19:49:27.451 DEBUG|              test:0395| after_iteration_hooks completed
08/01 19:49:27.452 WARNI|              test:0612| The test failed with the following exception
Traceback (most recent call last):
  File "/usr/local/autotest/common_lib/test.py", line 606, in _exec
    _call_test_function(self.execute, *p_args, **p_dargs)
  File "/usr/local/autotest/common_lib/test.py", line 806, in _call_test_function
    return func(*args, **dargs)
  File "/usr/local/autotest/common_lib/test.py", line 470, in execute
    dargs)
  File "/usr/local/autotest/common_lib/test.py", line 347, in _call_run_once_with_retry
    postprocess_profiled_run, args, dargs)
  File "/usr/local/autotest/common_lib/test.py", line 380, in _call_run_once
    self.run_once(*args, **dargs)
  File "/usr/local/autotest/tests/security_StatefulPermissions/security_StatefulPermissions.py", line 281, in run_once
    raise error.TestFail("Unexpected files/perms in stateful")
TestFail: Unexpected files/perms in stateful

This is the only error I find in the security_StatefulPermissions.ERROR log:
07/31 20:52:49.678 ERROR|security_StatefulP:0215| 520215    4 -rw-------   1 cryptohome cryptohome        8 Jul 31 20:31 /mnt/stateful_partition/unencrypted/preserve/attestation.epb.sum

And there is a recent change about the cryptohome merged in Jul 20. Not sure is this related?
https://chromium-review.googlesource.com/c/569016

Matthhew, can you take a look to see whether is this issue related to your change?