I think the issue is that once you start running a bunch of work chains in parallel on your local system, the CPU’s get overwhelmed quickly? As far as I know you can’t limit the number of active processes on a computer.
It seems you can install slurm with brew, but that might be overkill and a lot of work. It might also be an interesting use case of the HyperQueue scheduler, for which there is a plugin, but I’d have to try that out myself to see how (or if) it works.
If you can run one or a couple work chains together without issue, you could also consider writing a submission controller, so you could e.g. always keep two active work chains. Let me know if you need help with that, the documentation is still lacking.