Nodegrid allows 10 ssh connections enqueued during protocol negotiation phase. So if you launch more than 10 ssh sessions in parallel, there is a chance that some will be denied.
This is a regular approach taken by ssh daemon to prevent denial of service.
See MaxStartups parameter in sshd_config man page for more details.
If you launch 10 seasons first and allow a small delay to launch 10 more, all those session will be established just fine.