Time Over Theshold is not working

Document ID : KB000076438
Last Modified Date : 04/04/2018
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We have enabled Time Over Threshold and Sliding Window time to get alert of memory_physical_percent with threshold value of 3 Hours,

Alarm was generated even though in Performance Report we can see Physical Memory Percent did not go beyond 95% for 3 hours. 
upgraded nas to 9.0