So I solved the problem I had separately from the check_mask thing, but I though I’d just write what I did very explicitly.
The ocean_mask_table file input from ik11 says there are 24 masked domains (based on this). The current layout in &ocean_model_nml in input.nml is layout = 16, 15, so 16x15 - 24 masked = 216 cpus following this advice, and the model ran after changing that.
Not sure what to do with this so the people in charge can feel free to remove the post but since finding the number of masked domains was not obvious to me I thought I’d put this here anyways.