I have two different client IDs ("arduino1" and "arduino2"). I have also tried using only one unit powered at a time and it seems to be the same issue.
Strangely, I can't repeat this issue on my prototype board, which is identical in every way except the specific unit details (MAC, clientID, IP), and the fact that it's hooked up outside of the completed box. I've flashed all units multiple times with the same code, and it's still showing the same issue.