https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8934781651901984272

https://stainless.corp.google.com/browse/chromeos-autotest-results/240335091-chromeos-test/

...
09/21 06:20:27.826 ERROR|             utils:0287| [stderr] [0921/062026:INFO:update_engine_client.cc(486)] Forcing an update by setting app_version to ForcedUpdate.
09/21 06:20:27.826 ERROR|             utils:0287| [stderr] [0921/062026:INFO:update_engine_client.cc(488)] Initiating update check and install.
09/21 06:20:27.864 ERROR|             utils:0287| [stderr] [0921/062026:INFO:update_engine_client.cc(517)] Waiting for update to complete.
09/21 06:23:59.099 ERROR|             utils:0287| [stderr] [0921/062357:INFO:update_engine_client.cc(239)] Update succeeded -- reboot needed.
09/21 06:24:29.247 ERROR|             utils:0287| [stderr] Connection timed out during banner exchange
09/21 06:24:40.007 WARNI|              test:0606| The test failed with the following exception
Traceback (most recent call last):
  File "/usr/local/autotest/client/common_lib/test.py", line 600, in _exec
    _call_test_function(self.execute, *p_args, **p_dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 806, in _call_test_function
    raise error.UnhandledTestFail(e)
UnhandledTestFail: Unhandled AutoservRunError: command execution error
* Command: 
    /usr/bin/ssh -a -x   -o Protocol=2 -o StrictHostKeyChecking=no -o
    UserKnownHostsFile=/dev/null -o BatchMode=yes -o ConnectTimeout=30 -o
    ServerAliveInterval=900 -o ServerAliveCountMax=3 -o ConnectionAttempts=4
    -l root -p 22 chromeos4-row10-rack5-host11 "export LIBC_FATAL_STDERR_=1;
    if type \"logger\" > /dev/null 2>&1; then logger -tag \"autotest\"
    \"server[stack::_verify_update_completed|check_update_status|run] ->
    ssh_run(/usr/bin/update_engine_client -status | grep CURRENT_OP)\";fi;
    /usr/bin/update_engine_client -status | grep CURRENT_OP"
Exit status: 255
Duration: 30.0861170292

stderr:
Connection timed out during banner exchange
Traceback (most recent call last):
  File "/usr/local/autotest/client/common_lib/test.py", line 800, in _call_test_function
    return func(*args, **dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 464, in execute
    postprocess_profiled_run, args, dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 371, in _call_run_once
    self.run_once(*args, **dargs)
  File "/usr/local/autotest/server/site_tests/autoupdate_Rollback/autoupdate_Rollback.py", line 55, in run_once
    updater.update_image()
  File "/usr/local/autotest/server/cros/autoupdater.py", line 616, in update_image
    return self._verify_update_completed()
  File "/usr/local/autotest/server/cros/autoupdater.py", line 565, in _verify_update_completed
    status = self.check_update_status()
  File "/usr/local/autotest/server/cros/autoupdater.py", line 366, in check_update_status
    _UPDATER_BIN)
  File "/usr/local/autotest/server/hosts/ssh_host.py", line 335, in run
    return self.run_very_slowly(*args, **kwargs)
  File "/usr/local/autotest/server/hosts/ssh_host.py", line 324, in run_very_slowly
    ssh_failure_retry_ok)
  File "/usr/local/autotest/server/hosts/ssh_host.py", line 268, in _run
    raise error.AutoservRunError("command execution error", result)
AutoservRunError: command execution error
* Command: 
    /usr/bin/ssh -a -x   -o Protocol=2 -o StrictHostKeyChecking=no -o
    UserKnownHostsFile=/dev/null -o BatchMode=yes -o ConnectTimeout=30 -o
    ServerAliveInterval=900 -o ServerAliveCountMax=3 -o ConnectionAttempts=4
    -l root -p 22 chromeos4-row10-rack5-host11 "export LIBC_FATAL_STDERR_=1;
    if type \"logger\" > /dev/null 2>&1; then logger -tag \"autotest\"
    \"server[stack::_verify_update_completed|check_update_status|run] ->
    ssh_run(/usr/bin/update_engine_client -status | grep CURRENT_OP)\";fi;
    /usr/bin/update_engine_client -status | grep CURRENT_OP"
Exit status: 255
Duration: 30.0861170292

stderr:
Connection timed out during banner exchange
...

Looks like the device updated but failed to come back afterwards? Maybe a crash/hang flake?