I figured it out and it was a simple issue. I was controlling the rule through the Zen31 parent device, and the commands apparently stopped working at the parent level. If I go to the child device in the device listing and run the command there it works fine.
What I don't know is why this would have changed / stopped working for all the Zen31's at the same time. Like I said, I didn't change anything to initiate the issue.
Problem solved for the moment
