The error in the Release builders looks like:

cmd=['git', 'push', 'origin', 'temp_auto_checkin_branch:refs/heads/master'], cwd=/b/swarming/w/ir/cache/cbuild/repository/manifest-versions-internal
03:14:24: ERROR: Retrying to update the status:  Retry 1/20
03:14:24: INFO: Updating manifest-versions checkout.
03:15:10: INFO: Pushing to branch (_RemoteRef(remote='origin', ref='refs/heads/master', project_name=None)) with message: Automatic checkin: status=pass build_version 11151.85.0 for grunt-release 
03:15:10: ERROR: Failed to update the status for grunt-release during remote command: 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.

This is the first build run exhibiting this error: https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8927106603413760816

which makes me think it was likely caused by this chumped commit: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1378909

The initial report is something new; perhaps a Gerrit flake. Comment 1, however, is unrelated and is another example of  issue 791061 .

I think the chump here:
https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1394573

Is causing these errors in the CQ:

https://luci-logdog.appspot.com/logs/chromeos/buildbucket/cr-buildbucket.appspot.com/8925309464790329088/+/steps/CommitQueueSync/0/stdout

15:55:18: INFO: Translating result <class 'chromite.cbuildbot.manifest_version.GenerateBuildSpecException'>: Failed to generate LKGM Candidate. error: return code: 1; command: git push origin temp_auto_checkin_branch:refs/for/master%submit

To https://chromium.googlesource.com/a/chromiumos/manifest-versions
 ! [remote rejected]       temp_auto_checkin_branch -> refs/for/master%submit (commit dcc264a: missing Change-Id in message footer)
error: failed to push some refs to 'https://chromium.googlesource.com/a/chromiumos/manifest-versions'