Michael,
I'm having this problem as well. Currently running 4.5.1. Thought it was an error because I was running an older version so I updated to 4.5.1 and problem still persists. I'm getting the "not responding check power supply" over various devices but still able to command through admin console. Tried rebooting ISY as well as Echo rediscovery. Discovered everything fine but voice commands failed over multiple Echos. Do you have any suggestions or any other troubleshooting methods?
Thanks,
Larry