The following build got stuck for at least three hours in the CommitQueueSync stage.
https://uberchromegw.corp.google.com/i/chromeos/builders/master-paladin/builds/14667

Seems to be repeatedly syncing:
real	0m34.380s
06:57:54: INFO: RunCommand: repo --time sync --force-sync '--cache-dir=/b/build/slave/cache/git' -l in /b/cbuild/repository
Your sources have been sync'd successfully.
real	0m5.179s
06:58:00: INFO: Waiting for new CLs (37 minutes left)...
06:58:30: INFO: RunCommand: repo manifest in /b/cbuild/repository
06:58:30: INFO: RunCommand: repo init --repo-url https://chromium.googlesource.com/external/repo --manifest-url https://chrome-internal-review.googlesource.com/chromeos/manifest-internal --manifest-name official.xml --manifest-branch master in /b/cbuild/repository
repo has been initialized in /b/cbuild/repository
06:58:31: INFO: RunCommand: repo sync --help in /b/cbuild/repository
06:58:31: INFO: RunCommand: repo --time sync --force-sync '--cache-dir=/b/build/slave/cache/git' -n in /b/cbuild/repository
--

The Waiting for new CLs line appears every minute or so:
03:41:15: INFO: Waiting for new CLs (234 minutes left)...
03:42:26: INFO: Waiting for new CLs (233 minutes left)...
03:43:37: INFO: Waiting for new CLs (232 minutes left)...