If it differs from time to time then i would more search on the ESX side. But other option is that it is a problem inside the special agent with parsing the data from ESX. Here you can only test with a newer version of the special agent. I would setup a empty test site with actual 1.6 CMK version and only add the problematic ESX and test if also this happens in 1.6. If yes it is a problem of the ESX more likely then a CMK problem.