I have a theory for what’s going on. It seems that the supervisor starts all the other containers before binding to the HTTP port, so I think that if your container is fast enough, the supervisor API might not be available yet. I’m double checking that this is indeed the case, and if so we can update it to ensure that the API is available before the other containers start.
For now, can you try updating your script to retry various times if the connection is refused, waiting a bit before each retry? I believe that the supervisor will eventually start responding