Controlled shutdown doesn't seem to work on more than one broker in a cluster

I wrote a script (attached here) to basically round robin through the brokers in a cluster doing the following 2 operations on each of them -

1. Send the controlled shutdown admin command. If it succeeds
2. Restart the broker

What I've observed is that only one broker is able to finish the above successfully the first time around. For the rest of the iterations, no broker is able to shutdown using the admin command and every single time it fails with the error message stating the same number of leaders on every broker.