Running Coin maintenance server fails sometimes

vmbuilder@vmbuilder:~/qt-ci$ ./run_ci -m "Coin is down for production update. The service will come up shortly. -aakeskim"
Launching maintenance status page in tmux.
Traceback (most recent call last):
File "./run_ci", line 259, in <module>
runMaintenanceServer(message=args.maintenance)
File "./run_ci", line 191, in runMaintenanceServer
check_call(["tmux", "new-session", "-d", '-sci', '-n maintenance', "maintenance_www/maintenance_webserver.py --message \'%s\'" % message])
File "/usr/lib/python3.5/subprocess.py", line 581, in check_call
raise CalledProcessError(retcode, cmd)