If upstart showed a strong signal when you pressed the toggle then the switch was doing it's job and sending the link and that same link was reaching the CIM. If that much was true then it seems to me that the problem would be outside the switch but then you wouldn't expect swapping the switch to correct the problem. No matter as long as it's working now but it would be interesting to see if you can send a link from the troubled switch in it's new location.
Mike.