I had the same issue with two MX100's  with  active Directory enabled. Hitting the AD servers with WMI request and ponding the CPU's at a constant 98%. Logged a call to Meraki TAC with the issue. Resolution was to request Meraki TAC to reduce the WMI polling time from the MX to AD server from 5 seconds to 30 seconds. This has reduced AD server CPU's to 50 -58% utilization and the AD Meraki MX status now shows green OK and no yellow warning.   Hope this helps. ... View more