`convox app cancel` does not work, says "unimplemented"

Any time my local rack app gets stuck in an “updating” state, which happens when iterating on getting things working in the Dockerfile and convox.yml with my app, there is no way to cancel it and start over without deleting the app and re-creating the environment variables and rebuilding the image.

$ convox apps cancel
Cancelling my-app... ERROR: unimplemented

$ convox apps 
APP      STATUS    RELEASE   
my-app  updating  RMUSJORMGT

Is convox apps cancel just not implemented in Local? What is the recommended solution?

I can run convox start again without cancelling, but doing so often leads to errors such as this one, which I think may be related: ERROR: dial tcp: lookup api.convox.svc.cluster.local: too many open files

My theory is that the app’s state being stuck in “updating” and re-running is trying to run one instance on top of the other instead of cancelling it?