To help improve fairness in the Helium UI queue, a temporary maximum limit of 516 slots (processor cores) has been placed on this queue. This is an aggregate count of all slots used by a single user. This means that one user would only be able to run two 256 slot jobs simultaneously even if resources are available to run a third 256 slot job.
This is temporary, and the general scheduling policy will be reviewed at an upcoming meeting of the University of Iowa Helium/HPC policy committee where final decisions will be reached on how to mitigate situations wherein users dominate compute resources.
If you have feedback on this, the general scheduling policy or generally about this change, please don't hesitate to contact firstname.lastname@example.org.