From the provision log:
03/06 13:28:02.313 DEBUG|         host_info:0198| Committing HostInfo to store <autotest_lib.server.hosts.afe_store.AfeStore object at 0x7f0c518406d0>
03/06 13:28:02.344 INFO |         afe_store:0101| adding labels: set(['cros-version:cyan-release/R55-8872.67.0'])
03/06 13:28:02.347 DEBUG|        retry_util:0136| <type 'exceptions.TypeError'>(set(['cros-version:cyan-release/R55-8872.67.0']) is not JSON serializable)
03/06 13:28:12.379 DEBUG|        retry_util:0136| <type 'exceptions.TypeError'>(set(['cros-version:cyan-release/R55-8872.67.0']) is not JSON serializable)
03/06 13:28:32.480 DEBUG|        retry_util:0136| <type 'exceptions.TypeError'>(set(['cros-version:cyan-release/R55-8872.67.0']) is not JSON serializable)
03/06 13:29:12.579 DEBUG|        retry_util:0136| <type 'exceptions.TypeError'>(set(['cros-version:cyan-release/R55-8872.67.0']) is not JSON serializable)
03/06 13:30:32.675 DEBUG|        retry_util:0136| <type 'exceptions.TypeError'>(set(['cros-version:cyan-release/R55-8872.67.0']) is not JSON serializable)
03/06 13:33:02.347 DEBUG|              test:0389| Test failed due to Timeout occurred- waited 300 seconds.. Exception log follows the after_iteration_hooks.
03/06 13:33:02.348 DEBUG|              test:0392| starting after_iteration_hooks
03/06 13:33:02.348 DEBUG|              test:0395| after_iteration_hooks completed
03/06 13:33:02.359 WARNI|              test:0615| The test failed with the following exception
Traceback (most recent call last):
  File "/usr/local/autotest/client/common_lib/test.py", line 609, in _exec
    _call_test_function(self.execute, *p_args, **p_dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 823, in _call_test_function
    raise error.UnhandledTestFail(e)
UnhandledTestFail: Unhandled TimeoutError: Timeout occurred- waited 300 seconds.
Traceback (most recent call last):
  File "/usr/local/autotest/client/common_lib/test.py", line 817, in _call_test_function
    return func(*args, **dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 470, in execute
    dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 347, in _call_run_once_with_retry
    postprocess_profiled_run, args, dargs)
  File "/usr/local/autotest/client/common_lib/test.py", line 380, in _call_run_once
    self.run_once(*args, **dargs)
  File "/usr/local/autotest/server/site_tests/provision_AutoUpdate/provision_AutoUpdate.py", line 113, in run_once
    force_full_update=force)
  File "/usr/local/autotest/server/afe_utils.py", line 148, in machine_install_and_update_labels
    host.host_info_store.commit(info)
  File "/usr/local/autotest/server/hosts/host_info.py", line 200, in commit
    self._commit_impl(info)
  File "/usr/local/autotest/server/hosts/afe_store.py", line 65, in _commit_impl
    self._add_labels_on_afe(set(new_info.labels) - set(old_info.labels))
  File "/usr/local/autotest/server/hosts/afe_store.py", line 103, in _add_labels_on_afe
    self._afe.run('host_add_labels', id=self._hostname, labels=labels)
  File "/usr/local/autotest/server/cros/dynamic_suite/frontend_wrappers.py", line 111, in run
    self, call, **dargs)
  File "/usr/lib64/python2.7/site-packages/chromite/lib/retry_util.py", line 114, in GenericRetry
    time.sleep(sleep_time)
  File "/usr/lib64/python2.7/site-packages/chromite/lib/timeout_util.py", line 62, in kill_us
    raise TimeoutError(error_message % {'time': max_run_time})
TimeoutError: Timeout occurred- waited 300 seconds.


+Pprabhu as he had many CLs in the CQ

I think its likely this CLs fault:
https://chromium-review.googlesource.com/c/442826/

Yes. Already added to go/chromiumos-build-annotator :)