An instance is reporting encountering this error:
EXCEPTION: (CommandException) Command failed with error #1! COMMAND git fetch --prune -- '********' '+refs/*:refs/*' STDOUT (empty) STDERR error: Ref refs/heads/master is at <X> but expected <Y> From <origin> ! Y..X master -> master (unable to update local ref)
...where X and Y are commit hashes. This points at missing or inconsistent locking on some pathway where we run git fetch.